diff --git a/.travis.yml b/.travis.yml
index 008cbc167..b0e500072 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,3 +1,3 @@
 language: node_js
 node_js:
-  - "5.10.0"
+  - "12.18.2"
diff --git a/README.md b/README.md
index 7036f25d7..02ed0bcb0 100644
--- a/README.md
+++ b/README.md
@@ -29,8 +29,6 @@ To start javascript assignments please follow the next steps:
   git commit -m "Update the links"
   git push origin master
 ```
-* Open https://github.com/AisBrestEDU/js-assignments and test the build icon. Now it will run all tests and update status once you push changes to github. Keep this icon green!
-
 
 ### How to setup work environment
 * Download and install the latest [Nodejs](https://nodejs.org/en/download/stable/).
@@ -73,7 +71,6 @@ and run the unit tests again. Find one test failed (red). Now it's time to fix i
 * Implement the function by any way and verify your solution by running tests until the failed test become passed (green).
 * Your solution work, but now time to refactor it. Try to make your code as pretty and simple as possible keeping up the test green.
 * Once you can't improve your code and tests are passed you can commit your solution.
-* Push your updates to github server and check if tests passed on [travis-ci](https://travis-ci.org/AisBrestEDU/js-assignments/builds).
 * If everything is OK you can try to resolve the next task.
 
 ### How to debug tasks
diff --git a/package-lock.json b/package-lock.json
index c87f25cb9..b80890e47 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -40,21 +40,6 @@
             "escape-string-regexp": "^1.0.5",
             "supports-color": "^5.3.0"
           }
-        },
-        "escape-string-regexp": {
-          "version": "1.0.5",
-          "resolved": "https://registry.npmjs.org/escape-string-regexp/-/escape-string-regexp-1.0.5.tgz",
-          "integrity": "sha1-G2HAViGQqN/2rjuyzwIAyhMLhtQ=",
-          "dev": true
-        },
-        "supports-color": {
-          "version": "5.5.0",
-          "resolved": "https://registry.npmjs.org/supports-color/-/supports-color-5.5.0.tgz",
-          "integrity": "sha512-QjVjwdXIt408MIiAqCX4oUKsgU2EqAGzs2Ppkm4aQYbjm+ZEWEcW4SfFNTr4uMNZma0ey4f5lgLrkB0aX0QMow==",
-          "dev": true,
-          "requires": {
-            "has-flag": "^3.0.0"
-          }
         }
       }
     },
@@ -65,9 +50,9 @@
       "dev": true
     },
     "acorn": {
-      "version": "7.3.1",
-      "resolved": "https://registry.npmjs.org/acorn/-/acorn-7.3.1.tgz",
-      "integrity": "sha512-tLc0wSnatxAQHVHUapaHdz72pi9KUyHjq5KyHjGg9Y8Ifdc79pTh2XvI6I1/chZbnM7QtNKzh66ooDogPZSleA==",
+      "version": "7.4.0",
+      "resolved": "https://registry.npmjs.org/acorn/-/acorn-7.4.0.tgz",
+      "integrity": "sha512-+G7P8jJmCHr+S+cLfQxygbWhXy+8YTVGzAkpEbcLo2mLoL7tij/VG41QSHACSf5QgYRhMZYHuNc6drJaO0Da+w==",
       "dev": true
     },
     "acorn-jsx": {
@@ -77,9 +62,9 @@
       "dev": true
     },
     "ajv": {
-      "version": "6.12.3",
-      "resolved": "https://registry.npmjs.org/ajv/-/ajv-6.12.3.tgz",
-      "integrity": "sha512-4K0cK3L1hsqk9xIb2z9vs/XU+PGJZ9PNpJRDS9YLzmNdX6jmVPfamLvTJr0aDAusnHyCHO6MjzlkAsgtqp9teA==",
+      "version": "6.12.4",
+      "resolved": "https://registry.npmjs.org/ajv/-/ajv-6.12.4.tgz",
+      "integrity": "sha512-eienB2c9qVQs2KWexhkrdMLVDoIQCz5KSeLxwg9Lzk4DOfBtIK9PQwwufcsn1jjGuf9WZmqPMbGxOzfcuphJCQ==",
       "dev": true,
       "requires": {
         "fast-deep-equal": "^3.1.1",
@@ -362,9 +347,9 @@
       }
     },
     "debug": {
-      "version": "3.2.6",
-      "resolved": "https://registry.npmjs.org/debug/-/debug-3.2.6.tgz",
-      "integrity": "sha512-mel+jf7nrtEl5Pn1Qx46zARXKDpBbvzezse7p7LqINmdoIk8PYP5SySaxEmYv6TZ0JyEKA1hsCId6DIhgITtWQ==",
+      "version": "4.1.1",
+      "resolved": "https://registry.npmjs.org/debug/-/debug-4.1.1.tgz",
+      "integrity": "sha512-pYAIzeRo8J6KPEaJ0VWOh5Pzkbw/RetuzehGM7QRRX5he4fPHx2rdKMB256ehJCkX+XRQm16eZLqLNS8RSZXZw==",
       "dev": true,
       "requires": {
         "ms": "^2.1.1"
@@ -479,9 +464,9 @@
       "dev": true
     },
     "eslint": {
-      "version": "7.4.0",
-      "resolved": "https://registry.npmjs.org/eslint/-/eslint-7.4.0.tgz",
-      "integrity": "sha512-gU+lxhlPHu45H3JkEGgYhWhkR9wLHHEXC9FbWFnTlEkbKyZKWgWRLgf61E8zWmBuI6g5xKBph9ltg3NtZMVF8g==",
+      "version": "7.7.0",
+      "resolved": "https://registry.npmjs.org/eslint/-/eslint-7.7.0.tgz",
+      "integrity": "sha512-1KUxLzos0ZVsyL81PnRN335nDtQ8/vZUD6uMtWbF+5zDtjKcsklIi78XoE0MVL93QvWTu+E5y44VyyCsOMBrIg==",
       "dev": true,
       "requires": {
         "@babel/code-frame": "^7.0.0",
@@ -492,9 +477,9 @@
         "doctrine": "^3.0.0",
         "enquirer": "^2.3.5",
         "eslint-scope": "^5.1.0",
-        "eslint-utils": "^2.0.0",
-        "eslint-visitor-keys": "^1.2.0",
-        "espree": "^7.1.0",
+        "eslint-utils": "^2.1.0",
+        "eslint-visitor-keys": "^1.3.0",
+        "espree": "^7.2.0",
         "esquery": "^1.2.0",
         "esutils": "^2.0.2",
         "file-entry-cache": "^5.0.1",
@@ -508,7 +493,7 @@
         "js-yaml": "^3.13.1",
         "json-stable-stringify-without-jsonify": "^1.0.1",
         "levn": "^0.4.1",
-        "lodash": "^4.17.14",
+        "lodash": "^4.17.19",
         "minimatch": "^3.0.4",
         "natural-compare": "^1.4.0",
         "optionator": "^0.9.1",
@@ -520,32 +505,6 @@
         "table": "^5.2.3",
         "text-table": "^0.2.0",
         "v8-compile-cache": "^2.0.3"
-      },
-      "dependencies": {
-        "debug": {
-          "version": "4.1.1",
-          "resolved": "https://registry.npmjs.org/debug/-/debug-4.1.1.tgz",
-          "integrity": "sha512-pYAIzeRo8J6KPEaJ0VWOh5Pzkbw/RetuzehGM7QRRX5he4fPHx2rdKMB256ehJCkX+XRQm16eZLqLNS8RSZXZw==",
-          "dev": true,
-          "requires": {
-            "ms": "^2.1.1"
-          }
-        },
-        "minimatch": {
-          "version": "3.0.4",
-          "resolved": "https://registry.npmjs.org/minimatch/-/minimatch-3.0.4.tgz",
-          "integrity": "sha512-yJHVQEhyqPLUTgt9B83PXu6W3rx4MvvHvSUvToogpwoGDOUQ+yDrR0HRot+yOCdCO7u4hX3pWft6kWBBcqh0UA==",
-          "dev": true,
-          "requires": {
-            "brace-expansion": "^1.1.7"
-          }
-        },
-        "ms": {
-          "version": "2.1.2",
-          "resolved": "https://registry.npmjs.org/ms/-/ms-2.1.2.tgz",
-          "integrity": "sha512-sGkPx+VjMtmA6MX27oA4FBFELFCZZ4S4XqeGOXCv68tT+jb3vk/RyaKWP0PTKyWtmLSM0b+adUTEvbs1PEaH2w==",
-          "dev": true
-        }
       }
     },
     "eslint-scope": {
@@ -574,14 +533,14 @@
       "dev": true
     },
     "espree": {
-      "version": "7.1.0",
-      "resolved": "https://registry.npmjs.org/espree/-/espree-7.1.0.tgz",
-      "integrity": "sha512-dcorZSyfmm4WTuTnE5Y7MEN1DyoPYy1ZR783QW1FJoenn7RailyWFsq/UL6ZAAA7uXurN9FIpYyUs3OfiIW+Qw==",
+      "version": "7.3.0",
+      "resolved": "https://registry.npmjs.org/espree/-/espree-7.3.0.tgz",
+      "integrity": "sha512-dksIWsvKCixn1yrEXO8UosNSxaDoSYpq9reEjZSbHLpT5hpaCAKTLBwq0RHtLrIr+c0ByiYzWT8KTMRzoRCNlw==",
       "dev": true,
       "requires": {
-        "acorn": "^7.2.0",
+        "acorn": "^7.4.0",
         "acorn-jsx": "^5.2.0",
-        "eslint-visitor-keys": "^1.2.0"
+        "eslint-visitor-keys": "^1.3.0"
       }
     },
     "esprima": {
@@ -600,9 +559,9 @@
       },
       "dependencies": {
         "estraverse": {
-          "version": "5.1.0",
-          "resolved": "https://registry.npmjs.org/estraverse/-/estraverse-5.1.0.tgz",
-          "integrity": "sha512-FyohXK+R0vE+y1nHLoBM7ZTyqRpqAlhdZHCWIWEviFLiGB8b04H6bQs8G+XTthacvT8VuwvteiP7RJSxMs8UEw==",
+          "version": "5.2.0",
+          "resolved": "https://registry.npmjs.org/estraverse/-/estraverse-5.2.0.tgz",
+          "integrity": "sha512-BxbNGGNm0RyRYvUdHpIwv9IWzeM9XClbOxwoATuFdOE7ZE6wHL+HQ5T8hoPM+zHvmKzzsEqhgy0GrQ5X13afiQ==",
           "dev": true
         }
       }
@@ -975,9 +934,9 @@
       "dev": true
     },
     "inquirer": {
-      "version": "7.3.2",
-      "resolved": "https://registry.npmjs.org/inquirer/-/inquirer-7.3.2.tgz",
-      "integrity": "sha512-DF4osh1FM6l0RJc5YWYhSDB6TawiBRlbV9Cox8MWlidU218Tb7fm3lQTULyUJDfJ0tjbzl0W4q651mrCCEM55w==",
+      "version": "7.3.3",
+      "resolved": "https://registry.npmjs.org/inquirer/-/inquirer-7.3.3.tgz",
+      "integrity": "sha512-JG3eIAj5V9CwcGvuOmoo6LB9kbAYT8HXffUl6memuszlwDC/qvFAJw49XJ5NROSFNPxp3iQg1GqkFhaY/CR0IA==",
       "dev": true,
       "requires": {
         "ansi-escapes": "^4.2.1",
@@ -986,7 +945,7 @@
         "cli-width": "^3.0.0",
         "external-editor": "^3.0.3",
         "figures": "^3.0.0",
-        "lodash": "^4.17.16",
+        "lodash": "^4.17.19",
         "mute-stream": "0.0.8",
         "run-async": "^2.4.0",
         "rxjs": "^6.6.0",
@@ -1086,10 +1045,16 @@
       "integrity": "sha512-41Cifkg6e8TylSpdtTpeLVMqvSBEVzTttHvERD741+pnZ8ANv0004MRL43QKPDlK9cGvNp6NZWZUBlbGXYxxng==",
       "dev": true
     },
-    "is-regex": {
+    "is-plain-obj": {
       "version": "1.1.0",
-      "resolved": "https://registry.npmjs.org/is-regex/-/is-regex-1.1.0.tgz",
-      "integrity": "sha512-iI97M8KTWID2la5uYXlkbSDQIg4F6o1sYboZKKTDpnDQMLtUL86zxhgDet3Q2SriaYsyGqZ6Mn2SjbRKeLHdqw==",
+      "resolved": "https://registry.npmjs.org/is-plain-obj/-/is-plain-obj-1.1.0.tgz",
+      "integrity": "sha1-caUMhCnfync8kqOQpKA7OfzVHT4=",
+      "dev": true
+    },
+    "is-regex": {
+      "version": "1.1.1",
+      "resolved": "https://registry.npmjs.org/is-regex/-/is-regex-1.1.1.tgz",
+      "integrity": "sha512-1+QkEcxiLlB7VEyFtyBg94e08OAsvq7FUBgApTq/w2ymCLyKJgDPsybBENVtA7XCQEgEXxKPonG+mvYRxh/LIg==",
       "dev": true,
       "requires": {
         "has-symbols": "^1.0.1"
@@ -1192,9 +1157,9 @@
       }
     },
     "lodash": {
-      "version": "4.17.19",
-      "resolved": "https://registry.npmjs.org/lodash/-/lodash-4.17.19.tgz",
-      "integrity": "sha512-JNvd8XER9GQX0v2qJgsaN/mzFCNA5BRe/j8JN9d+tWyGLSodKQHKFicdwNYzWwI3wjRnaKPsGj1XkBjx/F96DQ==",
+      "version": "4.17.20",
+      "resolved": "https://registry.npmjs.org/lodash/-/lodash-4.17.20.tgz",
+      "integrity": "sha512-PlhdFcillOINfeV7Ni6oF1TAEayyZBoZ8bcshTHqOYJYlrqzRK5hagpagky5o4HfCzzd1TRkXPMFq6cKk9rGmA==",
       "dev": true
     },
     "log-symbols": {
@@ -1216,15 +1181,6 @@
             "escape-string-regexp": "^1.0.5",
             "supports-color": "^5.3.0"
           }
-        },
-        "supports-color": {
-          "version": "5.5.0",
-          "resolved": "https://registry.npmjs.org/supports-color/-/supports-color-5.5.0.tgz",
-          "integrity": "sha512-QjVjwdXIt408MIiAqCX4oUKsgU2EqAGzs2Ppkm4aQYbjm+ZEWEcW4SfFNTr4uMNZma0ey4f5lgLrkB0aX0QMow==",
-          "dev": true,
-          "requires": {
-            "has-flag": "^3.0.0"
-          }
         }
       }
     },
@@ -1243,6 +1199,12 @@
         "brace-expansion": "^1.1.7"
       }
     },
+    "minimist": {
+      "version": "1.2.5",
+      "resolved": "https://registry.npmjs.org/minimist/-/minimist-1.2.5.tgz",
+      "integrity": "sha512-FM9nNUYrRBAELZQT3xeZQ7fmMOBg6nWNmJKTcgsJeaLstP/UODVpGsr5OhXhhXg6f+qtJ8uiZ+PUxkDWcgIXLw==",
+      "dev": true
+    },
     "mkdirp": {
       "version": "0.5.5",
       "resolved": "https://registry.npmjs.org/mkdirp/-/mkdirp-0.5.5.tgz",
@@ -1250,20 +1212,12 @@
       "dev": true,
       "requires": {
         "minimist": "^1.2.5"
-      },
-      "dependencies": {
-        "minimist": {
-          "version": "1.2.5",
-          "resolved": "https://registry.npmjs.org/minimist/-/minimist-1.2.5.tgz",
-          "integrity": "sha512-FM9nNUYrRBAELZQT3xeZQ7fmMOBg6nWNmJKTcgsJeaLstP/UODVpGsr5OhXhhXg6f+qtJ8uiZ+PUxkDWcgIXLw==",
-          "dev": true
-        }
       }
     },
     "mocha": {
-      "version": "8.0.1",
-      "resolved": "https://registry.npmjs.org/mocha/-/mocha-8.0.1.tgz",
-      "integrity": "sha512-vefaXfdYI8+Yo8nPZQQi0QO2o+5q9UIMX1jZ1XMmK3+4+CQjc7+B0hPdUeglXiTlr8IHMVRo63IhO9Mzt6fxOg==",
+      "version": "8.1.1",
+      "resolved": "https://registry.npmjs.org/mocha/-/mocha-8.1.1.tgz",
+      "integrity": "sha512-p7FuGlYH8t7gaiodlFreseLxEmxTgvyG9RgPHODFPySNhwUehu8NIb0vdSt3WFckSneswZ0Un5typYcWElk7HQ==",
       "dev": true,
       "requires": {
         "ansi-colors": "4.1.1",
@@ -1282,7 +1236,7 @@
         "ms": "2.1.2",
         "object.assign": "4.1.0",
         "promise.allsettled": "1.0.2",
-        "serialize-javascript": "3.0.0",
+        "serialize-javascript": "4.0.0",
         "strip-json-comments": "3.0.1",
         "supports-color": "7.1.0",
         "which": "2.0.2",
@@ -1290,9 +1244,24 @@
         "workerpool": "6.0.0",
         "yargs": "13.3.2",
         "yargs-parser": "13.1.2",
-        "yargs-unparser": "1.6.0"
+        "yargs-unparser": "1.6.1"
       },
       "dependencies": {
+        "debug": {
+          "version": "3.2.6",
+          "resolved": "https://registry.npmjs.org/debug/-/debug-3.2.6.tgz",
+          "integrity": "sha512-mel+jf7nrtEl5Pn1Qx46zARXKDpBbvzezse7p7LqINmdoIk8PYP5SySaxEmYv6TZ0JyEKA1hsCId6DIhgITtWQ==",
+          "dev": true,
+          "requires": {
+            "ms": "^2.1.1"
+          }
+        },
+        "has-flag": {
+          "version": "4.0.0",
+          "resolved": "https://registry.npmjs.org/has-flag/-/has-flag-4.0.0.tgz",
+          "integrity": "sha512-EykJT/Q1KjTWctppgIAgfSO0tKVuZUjhgMr17kqTumMl6Afv3EISleU7qZUzoXDFTAHTDC4NOoG/ZxU3EvlMPQ==",
+          "dev": true
+        },
         "js-yaml": {
           "version": "3.13.1",
           "resolved": "https://registry.npmjs.org/js-yaml/-/js-yaml-3.13.1.tgz",
@@ -1308,6 +1277,15 @@
           "resolved": "https://registry.npmjs.org/strip-json-comments/-/strip-json-comments-3.0.1.tgz",
           "integrity": "sha512-VTyMAUfdm047mwKl+u79WIdrZxtFtn+nBxHeb844XBQ9uMNTuTHdx2hc5RiAJYqwTj3wc/xe5HLSdJSkJ+WfZw==",
           "dev": true
+        },
+        "supports-color": {
+          "version": "7.1.0",
+          "resolved": "https://registry.npmjs.org/supports-color/-/supports-color-7.1.0.tgz",
+          "integrity": "sha512-oRSIpR8pxT1Wr2FquTNnGet79b3BWljqOuoW/h4oBhxJ/HUbX5nX6JSruTkvXDCFMwDPvsaTTbvMLKZWSy0R5g==",
+          "dev": true,
+          "requires": {
+            "has-flag": "^4.0.0"
+          }
         }
       }
     },
@@ -1361,15 +1339,6 @@
             }
           }
         },
-        "debug": {
-          "version": "4.1.1",
-          "resolved": "https://registry.npmjs.org/debug/-/debug-4.1.1.tgz",
-          "integrity": "sha512-pYAIzeRo8J6KPEaJ0VWOh5Pzkbw/RetuzehGM7QRRX5he4fPHx2rdKMB256ehJCkX+XRQm16eZLqLNS8RSZXZw==",
-          "dev": true,
-          "requires": {
-            "ms": "^2.1.1"
-          }
-        },
         "eslint": {
           "version": "6.8.0",
           "resolved": "https://registry.npmjs.org/eslint/-/eslint-6.8.0.tgz",
@@ -1507,15 +1476,6 @@
             "ansi-regex": "^4.1.0"
           }
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-        "supports-color": {
-          "version": "5.5.0",
-          "resolved": "https://registry.npmjs.org/supports-color/-/supports-color-5.5.0.tgz",
-          "integrity": "sha512-QjVjwdXIt408MIiAqCX4oUKsgU2EqAGzs2Ppkm4aQYbjm+ZEWEcW4SfFNTr4uMNZma0ey4f5lgLrkB0aX0QMow==",
-          "dev": true,
-          "requires": {
-            "has-flag": "^3.0.0"
-          }
-        },
         "type-check": {
           "version": "0.3.2",
           "resolved": "https://registry.npmjs.org/type-check/-/type-check-0.3.2.tgz",
@@ -1600,9 +1560,9 @@
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     "onetime": {
-      "version": "5.1.0",
-      "resolved": "https://registry.npmjs.org/onetime/-/onetime-5.1.0.tgz",
-      "integrity": "sha512-5NcSkPHhwTVFIQN+TUqXoS5+dlElHXdpAWu9I0HP20YOtIi+aZ0Ct82jdlILDxjLEAWwvm+qj1m6aEtsDVmm6Q==",
+      "version": "5.1.2",
+      "resolved": "https://registry.npmjs.org/onetime/-/onetime-5.1.2.tgz",
+      "integrity": "sha512-kbpaSSGJTWdAY5KPVeMOKXSrPtr8C8C7wodJbcsd51jRnmD+GZu8Y0VoU6Dm5Z4vWr0Ig/1NKuWRKf7j5aaYSg==",
       "dev": true,
       "requires": {
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@@ -1716,6 +1676,15 @@
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       "dev": true
     },
+    "randombytes": {
+      "version": "2.1.0",
+      "resolved": "https://registry.npmjs.org/randombytes/-/randombytes-2.1.0.tgz",
+      "integrity": "sha512-vYl3iOX+4CKUWuxGi9Ukhie6fsqXqS9FE2Zaic4tNFD2N2QQaXOMFbuKK4QmDHC0JO6B1Zp41J0LpT0oR68amQ==",
+      "dev": true,
+      "requires": {
+        "safe-buffer": "^5.1.0"
+      }
+    },
     "readdirp": {
       "version": "3.3.0",
       "resolved": "https://registry.npmjs.org/readdirp/-/readdirp-3.3.0.tgz",
@@ -1772,31 +1741,6 @@
       "dev": true,
       "requires": {
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-      },
-      "dependencies": {
-        "glob": {
-          "version": "7.1.6",
-          "resolved": "https://registry.npmjs.org/glob/-/glob-7.1.6.tgz",
-          "integrity": "sha512-LwaxwyZ72Lk7vZINtNNrywX0ZuLyStrdDtabefZKAY5ZGJhVtgdznluResxNmPitE0SAO+O26sWTHeKSI2wMBA==",
-          "dev": true,
-          "requires": {
-            "fs.realpath": "^1.0.0",
-            "inflight": "^1.0.4",
-            "inherits": "2",
-            "minimatch": "^3.0.4",
-            "once": "^1.3.0",
-            "path-is-absolute": "^1.0.0"
-          }
-        },
-        "minimatch": {
-          "version": "3.0.4",
-          "resolved": "https://registry.npmjs.org/minimatch/-/minimatch-3.0.4.tgz",
-          "integrity": "sha512-yJHVQEhyqPLUTgt9B83PXu6W3rx4MvvHvSUvToogpwoGDOUQ+yDrR0HRot+yOCdCO7u4hX3pWft6kWBBcqh0UA==",
-          "dev": true,
-          "requires": {
-            "brace-expansion": "^1.1.7"
-          }
-        }
       }
     },
     "run-async": {
@@ -1806,14 +1750,20 @@
       "dev": true
     },
     "rxjs": {
-      "version": "6.6.0",
-      "resolved": "https://registry.npmjs.org/rxjs/-/rxjs-6.6.0.tgz",
-      "integrity": "sha512-3HMA8z/Oz61DUHe+SdOiQyzIf4tOx5oQHmMir7IZEu6TMqCLHT4LRcmNaUS0NwOz8VLvmmBduMsoaUvMaIiqzg==",
+      "version": "6.6.2",
+      "resolved": "https://registry.npmjs.org/rxjs/-/rxjs-6.6.2.tgz",
+      "integrity": "sha512-BHdBMVoWC2sL26w//BCu3YzKT4s2jip/WhwsGEDmeKYBhKDZeYezVUnHatYB7L85v5xs0BAQmg6BEYJEKxBabg==",
       "dev": true,
       "requires": {
         "tslib": "^1.9.0"
       }
     },
+    "safe-buffer": {
+      "version": "5.2.1",
+      "resolved": "https://registry.npmjs.org/safe-buffer/-/safe-buffer-5.2.1.tgz",
+      "integrity": "sha512-rp3So07KcdmmKbGvgaNxQSJr7bGVSVk5S9Eq1F+ppbRo70+YeaDxkw5Dd8NPN+GD6bjnYm2VuPuCXmpuYvmCXQ==",
+      "dev": true
+    },
     "safer-buffer": {
       "version": "2.1.2",
       "resolved": "https://registry.npmjs.org/safer-buffer/-/safer-buffer-2.1.2.tgz",
@@ -1827,10 +1777,13 @@
       "dev": true
     },
     "serialize-javascript": {
-      "version": "3.0.0",
-      "resolved": "https://registry.npmjs.org/serialize-javascript/-/serialize-javascript-3.0.0.tgz",
-      "integrity": "sha512-skZcHYw2vEX4bw90nAr2iTTsz6x2SrHEnfxgKYmZlvJYBEZrvbKtobJWlQ20zczKb3bsHHXXTYt48zBA7ni9cw==",
-      "dev": true
+      "version": "4.0.0",
+      "resolved": "https://registry.npmjs.org/serialize-javascript/-/serialize-javascript-4.0.0.tgz",
+      "integrity": "sha512-GaNA54380uFefWghODBWEGisLZFj00nS5ACs6yHa9nLqlLpVLO8ChDGeKRjZnV4Nh4n0Qi7nhYZD/9fCPzEqkw==",
+      "dev": true,
+      "requires": {
+        "randombytes": "^2.1.0"
+      }
     },
     "set-blocking": {
       "version": "2.0.0",
@@ -1940,20 +1893,12 @@
       "dev": true
     },
     "supports-color": {
-      "version": "7.1.0",
-      "resolved": "https://registry.npmjs.org/supports-color/-/supports-color-7.1.0.tgz",
-      "integrity": "sha512-oRSIpR8pxT1Wr2FquTNnGet79b3BWljqOuoW/h4oBhxJ/HUbX5nX6JSruTkvXDCFMwDPvsaTTbvMLKZWSy0R5g==",
+      "version": "5.5.0",
+      "resolved": "https://registry.npmjs.org/supports-color/-/supports-color-5.5.0.tgz",
+      "integrity": "sha512-QjVjwdXIt408MIiAqCX4oUKsgU2EqAGzs2Ppkm4aQYbjm+ZEWEcW4SfFNTr4uMNZma0ey4f5lgLrkB0aX0QMow==",
       "dev": true,
       "requires": {
-        "has-flag": "^4.0.0"
-      },
-      "dependencies": {
-        "has-flag": {
-          "version": "4.0.0",
-          "resolved": "https://registry.npmjs.org/has-flag/-/has-flag-4.0.0.tgz",
-          "integrity": "sha512-EykJT/Q1KjTWctppgIAgfSO0tKVuZUjhgMr17kqTumMl6Afv3EISleU7qZUzoXDFTAHTDC4NOoG/ZxU3EvlMPQ==",
-          "dev": true
-        }
+        "has-flag": "^3.0.0"
       }
     },
     "table": {
@@ -2211,14 +2156,81 @@
       }
     },
     "yargs-unparser": {
-      "version": "1.6.0",
-      "resolved": "https://registry.npmjs.org/yargs-unparser/-/yargs-unparser-1.6.0.tgz",
-      "integrity": "sha512-W9tKgmSn0DpSatfri0nx52Joq5hVXgeLiqR/5G0sZNDoLZFOr/xjBUDcShCOGNsBnEMNo1KAMBkTej1Hm62HTw==",
+      "version": "1.6.1",
+      "resolved": "https://registry.npmjs.org/yargs-unparser/-/yargs-unparser-1.6.1.tgz",
+      "integrity": "sha512-qZV14lK9MWsGCmcr7u5oXGH0dbGqZAIxTDrWXZDo5zUr6b6iUmelNKO6x6R1dQT24AH3LgRxJpr8meWy2unolA==",
       "dev": true,
       "requires": {
+        "camelcase": "^5.3.1",
+        "decamelize": "^1.2.0",
         "flat": "^4.1.0",
-        "lodash": "^4.17.15",
-        "yargs": "^13.3.0"
+        "is-plain-obj": "^1.1.0",
+        "yargs": "^14.2.3"
+      },
+      "dependencies": {
+        "find-up": {
+          "version": "3.0.0",
+          "resolved": "https://registry.npmjs.org/find-up/-/find-up-3.0.0.tgz",
+          "integrity": "sha512-1yD6RmLI1XBfxugvORwlck6f75tYL+iR0jqwsOrOxMZyGYqUuDhJ0l4AXdO1iX/FTs9cBAMEk1gWSEx1kSbylg==",
+          "dev": true,
+          "requires": {
+            "locate-path": "^3.0.0"
+          }
+        },
+        "locate-path": {
+          "version": "3.0.0",
+          "resolved": "https://registry.npmjs.org/locate-path/-/locate-path-3.0.0.tgz",
+          "integrity": "sha512-7AO748wWnIhNqAuaty2ZWHkQHRSNfPVIsPIfwEOWO22AmaoVrWavlOcMR5nzTLNYvp36X220/maaRsrec1G65A==",
+          "dev": true,
+          "requires": {
+            "p-locate": "^3.0.0",
+            "path-exists": "^3.0.0"
+          }
+        },
+        "p-locate": {
+          "version": "3.0.0",
+          "resolved": "https://registry.npmjs.org/p-locate/-/p-locate-3.0.0.tgz",
+          "integrity": "sha512-x+12w/To+4GFfgJhBEpiDcLozRJGegY+Ei7/z0tSLkMmxGZNybVMSfWj9aJn8Z5Fc7dBUNJOOVgPv2H7IwulSQ==",
+          "dev": true,
+          "requires": {
+            "p-limit": "^2.0.0"
+          }
+        },
+        "path-exists": {
+          "version": "3.0.0",
+          "resolved": "https://registry.npmjs.org/path-exists/-/path-exists-3.0.0.tgz",
+          "integrity": "sha1-zg6+ql94yxiSXqfYENe1mwEP1RU=",
+          "dev": true
+        },
+        "yargs": {
+          "version": "14.2.3",
+          "resolved": "https://registry.npmjs.org/yargs/-/yargs-14.2.3.tgz",
+          "integrity": "sha512-ZbotRWhF+lkjijC/VhmOT9wSgyBQ7+zr13+YLkhfsSiTriYsMzkTUFP18pFhWwBeMa5gUc1MzbhrO6/VB7c9Xg==",
+          "dev": true,
+          "requires": {
+            "cliui": "^5.0.0",
+            "decamelize": "^1.2.0",
+            "find-up": "^3.0.0",
+            "get-caller-file": "^2.0.1",
+            "require-directory": "^2.1.1",
+            "require-main-filename": "^2.0.0",
+            "set-blocking": "^2.0.0",
+            "string-width": "^3.0.0",
+            "which-module": "^2.0.0",
+            "y18n": "^4.0.0",
+            "yargs-parser": "^15.0.1"
+          }
+        },
+        "yargs-parser": {
+          "version": "15.0.1",
+          "resolved": "https://registry.npmjs.org/yargs-parser/-/yargs-parser-15.0.1.tgz",
+          "integrity": "sha512-0OAMV2mAZQrs3FkNpDQcBk1x5HXb8X4twADss4S0Iuk+2dGnLOE/fRHrsYm542GduMveyA77OF4wrNJuanRCWw==",
+          "dev": true,
+          "requires": {
+            "camelcase": "^5.0.0",
+            "decamelize": "^1.2.0"
+          }
+        }
       }
     }
   }
diff --git a/package.json b/package.json
index 1830b3015..281a7cdd0 100644
--- a/package.json
+++ b/package.json
@@ -3,7 +3,7 @@
   "version": "0.9.1",
   "description": "JS training tasks",
   "engines": {
-    "node": "^10.0.0"
+    "node": "^5.10.0"
   },
   "scripts": {
     "test": "./node_modules/.bin/mocha",
diff --git a/task/01-strings-tasks.js b/task/01-strings-tasks.js
index e28054657..95feb69b7 100644
--- a/task/01-strings-tasks.js
+++ b/task/01-strings-tasks.js
@@ -22,7 +22,7 @@
  *   '',  'bb'  => 'bb'
  */
 function concatenateStrings(value1, value2) {
-    throw new Error('Not implemented');
+    return value1 + value2;
 }
 
 
@@ -38,7 +38,7 @@ function concatenateStrings(value1, value2) {
  *   ''      => 0
  */
 function getStringLength(value) {
-    throw new Error('Not implemented');
+    return value.length;
 }
 
 /**
@@ -55,7 +55,7 @@ function getStringLength(value) {
  *   'Chuck','Norris'  => 'Hello, Chuck Norris!'
  */
 function getStringFromTemplate(firstName, lastName) {
-    throw new Error('Not implemented');
+    return `Hello, ${firstName} ${lastName}!`;
 }
 
 /**
@@ -69,7 +69,7 @@ function getStringFromTemplate(firstName, lastName) {
  *   'Hello, Chuck Norris!' => 'Chuck Norris'
  */
 function extractNameFromTemplate(value) {
-    throw new Error('Not implemented');
+    return value.substring(7, value.length - 1);
 }
 
 
@@ -84,7 +84,7 @@ function extractNameFromTemplate(value) {
  *   'cat'       => 'c'
  */
 function getFirstChar(value) {
-    throw new Error('Not implemented');
+    return value[0];
 }
 
 /**
@@ -99,7 +99,7 @@ function getFirstChar(value) {
  *   '\tHello, World! ' => 'Hello, World!'
  */
 function removeLeadingAndTrailingWhitespaces(value) {
-    throw new Error('Not implemented');
+    return value.trim();
 }
 
 /**
@@ -114,7 +114,7 @@ function removeLeadingAndTrailingWhitespaces(value) {
  *   'cat', 3 => 'catcatcat'
  */
 function repeatString(value, count) {
-    throw new Error('Not implemented');
+    return value.repeat(count);
 }
 
 /**
@@ -130,7 +130,14 @@ function repeatString(value, count) {
  *   'ABABAB','BA' => 'ABAB'
  */
 function removeFirstOccurrences(str, value) {
-    throw new Error('Not implemented');
+    let newStr = '';
+
+    if (str.indexOf(value)) {
+        newStr = str.slice(0, str.indexOf(value));
+        newStr += str.slice(str.indexOf(value) + value.length, str.length);
+    }
+
+    return newStr;
 }
 
 /**
@@ -145,7 +152,7 @@ function removeFirstOccurrences(str, value) {
  *   '<a>' => 'a'
  */
 function unbracketTag(str) {
-    throw new Error('Not implemented');
+    return str.substring(1, str.length - 1);
 }
 
 
@@ -160,7 +167,7 @@ function unbracketTag(str) {
  *  'abcdefghijklmnopqrstuvwxyz' => 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'
  */
 function convertToUpperCase(str) {
-    throw new Error('Not implemented');
+    return str.toUpperCase();
 }
 
 /**
@@ -174,7 +181,7 @@ function convertToUpperCase(str) {
  *   'info@gmail.com' => ['info@gmail.com']
  */
 function extractEmails(str) {
-    throw new Error('Not implemented');
+    return str.split(';');
 }
 
 /**
@@ -201,7 +208,21 @@ function extractEmails(str) {
  *
  */
 function getRectangleString(width, height) {
-    throw new Error('Not implemented');
+    let string = "";
+
+    for (let i = 1; i <= height; i++) {
+        if (i === 1) {
+            string = string + "┌" + "─".repeat(width - 2) + "┐\n";
+        }
+        if (i > 1 && i < height) {
+            string = string + "│" + " ".repeat(width - 2) + "│\n";
+        }
+        if (i === height) {
+            string = string + "└" + "─".repeat(width - 2) + "┘\n"
+        }
+    }
+
+    return string;
 }
 
 
@@ -221,7 +242,17 @@ function getRectangleString(width, height) {
  *
  */
 function encodeToRot13(str) {
-    throw new Error('Not implemented');
+    let string = '';
+
+    for (let i = 0; i < str.length; i++) {
+        if (((str.codePointAt(i) >= 65) && (str.codePointAt(i) <= 77)) || ((str.codePointAt(i) >= 97) && (str.codePointAt(i) <= 109))) {
+            string += String.fromCodePoint(str.codePointAt(i) + 13);
+        } else if (((str.codePointAt(i) < 65) || (str.codePointAt(i) > 90)) && ((str.codePointAt(i) < 97) || (str.codePointAt(i) > 122))) {
+            string += str[i];
+        } else string += String.fromCodePoint(str.codePointAt(i) - 13)
+    }
+
+    return string;
 }
 
 /**
@@ -238,7 +269,7 @@ function encodeToRot13(str) {
  *   isString(new String('test')) => true
  */
 function isString(value) {
-    throw new Error('Not implemented');
+    return typeof value === 'string' || value instanceof String;
 }
 
 
@@ -266,8 +297,20 @@ function isString(value) {
  *   'Q♠' => 50
  *   'K♠' => 51
  */
+
 function getCardId(value) {
-    throw new Error('Not implemented');
+    const arr = ['A', '2', '3', '4', '5', '6', '7', '8', '9', '10', 'J', 'Q', 'K'];
+
+    switch (value[value.length - 1]) {
+        case '♣':
+            return arr.indexOf(value.slice(0, -1));
+        case '♦':
+            return +(arr.indexOf(value.slice(0, -1))) + 13;
+        case '♥':
+            return +(arr.indexOf(value.slice(0, -1))) + 26;
+        case '♠':
+            return +(arr.indexOf(value.slice(0, -1))) + 39;
+    }
 }
 
 
diff --git a/task/02-numbers-tasks.js b/task/02-numbers-tasks.js
index c9ed20208..d920034b7 100644
--- a/task/02-numbers-tasks.js
+++ b/task/02-numbers-tasks.js
@@ -22,7 +22,7 @@
  *   5, 5  => 25
  */
 function getRectangleArea(width, height) {
-    throw new Error('Not implemented');
+    return width * height;
 }
 
 
@@ -38,7 +38,7 @@ function getRectangleArea(width, height) {
  *   0    => 0
  */
 function getCicleCircumference(radius) {
-    throw new Error('Not implemented');
+    return 2 * Math.PI * radius;
 }
 
 /**
@@ -54,7 +54,7 @@ function getCicleCircumference(radius) {
  *  -3, 3  => 0
  */
 function getAverage(value1, value2) {
-    throw new Error('Not implemented');
+    return value1 / 2 + value2 / 2;
 }
 
 /**
@@ -73,7 +73,7 @@ function getAverage(value1, value2) {
  *   (-5,0) (10,-10) => 18.027756377319946
  */
 function getDistanceBetweenPoints(x1, y1, x2, y2) {
-    throw new Error('Not implemented');
+    return Math.hypot(x2 - x1, y2 - y1);
 }
 
 /**
@@ -89,7 +89,7 @@ function getDistanceBetweenPoints(x1, y1, x2, y2) {
  *   5*x = 0         => 0
  */
 function getLinearEquationRoot(a, b) {
-    throw new Error('Not implemented');
+   return -b / a;
 }
 
 
@@ -111,7 +111,13 @@ function getLinearEquationRoot(a, b) {
  *   (0,1) (1,2)     => 0
  */
 function getAngleBetweenVectors(x1, y1, x2, y2) {
-    throw new Error('Not implemented');
+    const scalarProduct = (x1 * x2) + (y1 * y2);
+    const vectorProductX = Math.hypot(x1, y1);
+    const vectorProductY = Math.hypot(x2, y2);
+
+    let result = scalarProduct / (vectorProductX * vectorProductY);
+
+    return Math.acos(result);
 }
 
 /**
@@ -127,7 +133,7 @@ function getAngleBetweenVectors(x1, y1, x2, y2) {
  *     0     => 0
  */
 function getLastDigit(value) {
-    throw new Error('Not implemented');
+    return +value.toString().split('').pop();
 }
 
 
@@ -143,7 +149,7 @@ function getLastDigit(value) {
  * '-525.5'     => -525.5
  */
 function parseNumberFromString(value) {
-    throw new Error('Not implemented');
+    return +value;
 }
 
 /**
@@ -159,8 +165,9 @@ function parseNumberFromString(value) {
  *   3,3,3   => 5.196152422706632
  *   1,2,3   => 3.741657386773941
  */
-function getParallelipidedDiagonal(a,b,c) {
-    throw new Error('Not implemented');
+function getParallelipidedDiagonal(a, b, c) {
+    return Math.sqrt(Math.pow(a, 2) + Math.pow(b, 2) + Math.pow(c, 2));
+    //return Math.sqrt(a ** 2 + b ** 2 + c ** 2);
 }
 
 /**
@@ -181,7 +188,11 @@ function getParallelipidedDiagonal(a,b,c) {
  *   1678, 3  => 2000
  */
 function roundToPowerOfTen(num, pow) {
-    throw new Error('Not implemented');
+    if (pow > 0) {
+        let newNum = '1' + '0'.repeat(pow);
+        return Math.round(num / newNum) * newNum;
+    }
+    return num;
 }
 
 /**
@@ -202,7 +213,15 @@ function roundToPowerOfTen(num, pow) {
  *   17 => true
  */
 function isPrime(n) {
-    throw new Error('Not implemented');
+    let result = true;
+
+    for (let i = n - 1; i > 1; i--) {
+        if (n % i === 0) {
+            result = false;
+            break;
+        }
+    }
+    return result;
 }
 
 /**
@@ -221,7 +240,8 @@ function isPrime(n) {
  *   toNumber(new Number(42), 0) => 42
  */
 function toNumber(value, def) {
-    throw new Error('Not implemented');
+    return parseInt(value, 10) || def;
+    //return (isFinite(value) && (value !== null)) ? value.valueOf() : def;
 }
 
 module.exports = {
diff --git a/task/03-date-tasks.js b/task/03-date-tasks.js
index 83c6266bc..6e5d18fb1 100644
--- a/task/03-date-tasks.js
+++ b/task/03-date-tasks.js
@@ -22,7 +22,7 @@
  *    'Sun, 17 May 1998 03:00:00 GMT+01' => Date()
  */
 function parseDataFromRfc2822(value) {
-   throw new Error('Not implemented');
+   return Date.parse(value);
 }
 
 /**
@@ -37,7 +37,7 @@ function parseDataFromRfc2822(value) {
  *    '2016-01-19T08:07:37Z' => Date()
  */
 function parseDataFromIso8601(value) {
-   throw new Error('Not implemented');
+   return Date.parse(value);
 }
 
 
@@ -56,7 +56,7 @@ function parseDataFromIso8601(value) {
  *    Date(2015,1,1)    => false
  */
 function isLeapYear(date) {
-   throw new Error('Not implemented');
+   return ((date.getFullYear() % 4 !== 0) || (date.getFullYear() % 100 === 0) && (date.getFullYear() % 400 !== 0)) ? false : true
 }
 
 
@@ -76,7 +76,32 @@ function isLeapYear(date) {
  *    Date(2000,1,1,10,0,0),  Date(2000,1,1,15,20,10,453)   => "05:20:10.453"
  */
 function timeSpanToString(startDate, endDate) {
-   throw new Error('Not implemented');
+   const timespanInMs = endDate.getTime() - startDate.getTime();
+   let milliseconds = Math.abs(timespanInMs);
+   const days = Math.floor(milliseconds / (1000 * 60 * 60 * 24));
+
+   milliseconds -= days * (1000 * 60 * 60 * 24);
+
+   let hours = Math.floor(milliseconds / (1000 * 60 * 60));
+   milliseconds -= hours * (1000 * 60 * 60);
+
+   const mins = Math.floor(milliseconds / (1000 * 60));
+   milliseconds -= mins * (1000 * 60);
+
+   const seconds = Math.floor(milliseconds / (1000));
+   milliseconds -= seconds * (1000);
+   const formatToDoubleDigit = (number) => number < 10 ? `0${number}` : `${number}`;
+   const formatToThreeDigit = (number) => {
+      if (number < 10) {
+         return `00${number}`;
+      } else if (number > 10 && number < 100) {
+         return `0${number}`;
+      }
+      return number;
+   }
+   hours = days * 24 + hours;
+   const result = `${formatToDoubleDigit(hours)}:${formatToDoubleDigit(mins)}:${formatToDoubleDigit(seconds)}.${formatToThreeDigit(milliseconds)}`
+   return result;
 }
 
 
@@ -94,14 +119,20 @@ function timeSpanToString(startDate, endDate) {
  *    Date.UTC(2016,3,5,21, 0) => Math.PI/2
  */
 function angleBetweenClockHands(date) {
-    throw new Error('Not implemented');
+   const currentDate = new Date(date);
+   const currentHors = (currentDate.getUTCHours() > 12) ? currentDate.getUTCHours() - 12 : currentDate.getUTCHours();
+   const angleBetweenClockHandsInDegrees = 0.5 * (60 * currentHors - 11 * currentDate.getUTCMinutes())
+   const result = angleBetweenClockHandsInDegrees > 180 ? 360 - angleBetweenClockHandsInDegrees : angleBetweenClockHandsInDegrees;
+
+   return Math.PI / 180 * Math.abs(result);
 }
 
 
+
 module.exports = {
-    parseDataFromRfc2822: parseDataFromRfc2822,
-    parseDataFromIso8601: parseDataFromIso8601,
-    isLeapYear: isLeapYear,
-    timeSpanToString: timeSpanToString,
-    angleBetweenClockHands: angleBetweenClockHands
+   parseDataFromRfc2822: parseDataFromRfc2822,
+   parseDataFromIso8601: parseDataFromIso8601,
+   isLeapYear: isLeapYear,
+   timeSpanToString: timeSpanToString,
+   angleBetweenClockHands: angleBetweenClockHands
 };
diff --git a/task/04-arrays-tasks.js b/task/04-arrays-tasks.js
index ff3a4c019..199646753 100644
--- a/task/04-arrays-tasks.js
+++ b/task/04-arrays-tasks.js
@@ -9,7 +9,7 @@
  *                                                                                           *
  *********************************************************************************************/
 
- 
+
 /**
  * Returns an index of the specified element in array or -1 if element is not found
  * 
@@ -23,7 +23,7 @@
  *    [0, 1, 2, 3, 4, 5], 5    => 5
  */
 function findElement(arr, value) {
-   throw new Error('Not implemented');
+   return arr.findIndex(item => item === value);
 }
 
 /**
@@ -38,7 +38,11 @@ function findElement(arr, value) {
  *    5 => [ 1, 3, 5, 7, 9 ]
  */
 function generateOdds(len) {
-   throw new Error('Not implemented');
+   let arr = Array(len).fill(1, 0, len);
+   return arr.map((item, index) => {
+      item = index * 2 + 1;
+      return item;
+   });
 }
 
 
@@ -54,7 +58,7 @@ function generateOdds(len) {
  *    [] => [] 
  */
 function doubleArray(arr) {
-   throw new Error('Not implemented');
+   return arr.concat(arr);
 }
 
 
@@ -70,7 +74,7 @@ function doubleArray(arr) {
  *    [] => [] 
  */
 function getArrayOfPositives(arr) {
-   throw new Error('Not implemented');
+   return arr.filter(item => item > 0);
 }
 
 /**
@@ -85,7 +89,7 @@ function getArrayOfPositives(arr) {
  *    [ 'cat, 'dog', 'raccon' ] => [ 'cat', 'dog', 'racoon' ]
  */
 function getArrayOfStrings(arr) {
-   throw new Error('Not implemented');
+   return arr.filter(item => typeof item === typeof String.name)
 }
 
 /**
@@ -102,7 +106,7 @@ function getArrayOfStrings(arr) {
  *    [ false, 0, NaN, '', undefined ]   => [ ]
  */
 function removeFalsyValues(arr) {
-   throw new Error('Not implemented');
+   return arr.filter(item => Boolean(item));
 }
 
 /**
@@ -116,7 +120,7 @@ function removeFalsyValues(arr) {
  *    [ 'a', 'b', 'c', 'd', 'e', 'f', 'g' ]  => [ 'A', 'B', 'C', 'D', 'E', 'F', 'G' ]
  */
 function getUpperCaseStrings(arr) {
-   throw new Error('Not implemented');
+   return arr.join().toUpperCase().split(',');
 }
 
 
@@ -131,7 +135,7 @@ function getUpperCaseStrings(arr) {
  *    [ 'angular', 'react', 'ember' ] => [ 7, 5, 5 ]
  */
 function getStringsLength(arr) {
-   throw new Error('Not implemented');
+   return arr.map(item => item.length);
 }
 
 /**
@@ -146,7 +150,7 @@ function getStringsLength(arr) {
  *    [ 1, 'b', 'c'], 0, 'x'  => [ 'x', 1, 'b', 'c' ]
  */
 function insertItem(arr, item, index) {
-   throw new Error('Not implemented');
+   return arr.splice(index, 0, item);
 }
 
 /**
@@ -160,7 +164,7 @@ function insertItem(arr, item, index) {
  *    [ 'a', 'b', 'c', 'd'], 3  => [ 'a', 'b', 'c' ]
  */
 function getHead(arr, n) {
-   throw new Error('Not implemented');
+   return arr.slice(0, n);
 }
 
 
@@ -175,7 +179,7 @@ function getHead(arr, n) {
  *    [ 'a', 'b', 'c', 'd'], 3  => [ 'b', 'c', 'd' ]
  */
 function getTail(arr, n) {
-   throw new Error('Not implemented');
+   return arr.slice(-n);
 }
 
 
@@ -200,7 +204,7 @@ function getTail(arr, n) {
  *    +'30,31,32,33,34'
  */
 function toCsvText(arr) {
-   throw new Error('Not implemented');
+   return arr.map(item => item.join() + '\n').join('').slice(0, -1)
 }
 
 /**
@@ -215,7 +219,7 @@ function toCsvText(arr) {
  *   [ 10, 100, -1 ]      => [ 100, 10000, 1 ]
  */
 function toArrayOfSquares(arr) {
-   throw new Error('Not implemented');
+   return arr.map(item => Math.pow(item, 2));
 }
 
 
@@ -234,9 +238,16 @@ function toArrayOfSquares(arr) {
  *   [ 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 ] => [ 1, 3, 6, 10, 15, 21, 28, 36, 45, 55 ]
  */
 function getMovingSum(arr) {
-   throw new Error('Not implemented');
-}
+   const newArr = [];
+
+   arr.map((item, index) => {
+      if (!index) {
+         newArr.push(item);
+      } else newArr.push(newArr[index - 1] + item)
+   })
 
+   return newArr;
+}
 /**
  * Returns every second item from the specified array:
  * 
@@ -249,10 +260,9 @@ function getMovingSum(arr) {
  * [ "a" ] => []
  */
 function getSecondItems(arr) {
-   throw new Error('Not implemented');
+   return arr.filter((item, index) => (index % 2));
 }
 
-
 /**
  * Propagates every item in sequence its position times
  * Returns an array that consists of: one first item, two second items, tree third items etc. 
@@ -268,7 +278,13 @@ function getSecondItems(arr) {
  *  [ 1,2,3,4,5 ] => [ 1, 2,2, 3,3,3, 4,4,4,4, 5,5,5,5,5 ]
  */
 function propagateItemsByPositionIndex(arr) {
-   throw new Error('Not implemented');
+   const finalArray = [];
+   arr.filter((elem, index) => {
+      const arrayOfIdenticalNumbers = new Array(index + 1);
+      arrayOfIdenticalNumbers.fill(elem);
+      finalArray.push(...arrayOfIdenticalNumbers);
+   });
+   return finalArray;
 }
 
 
@@ -286,10 +302,10 @@ function propagateItemsByPositionIndex(arr) {
  *   [ 10, 10, 10, 10 ] => [ 10, 10, 10 ]
  */
 function get3TopItems(arr) {
-   throw new Error('Not implemented');
+   return (arr.length <= 3) ? arr.sort((a, b) => b - a) : arr.sort((a, b) => b - a).slice(0, 3);
 }
- 
- 
+
+
 /**  
  * Returns the number of positive numbers from specified array
  * 
@@ -304,9 +320,9 @@ function get3TopItems(arr) {
  *   [ 1, '2' ] => 1
  */
 function getPositivesCount(arr) {
-   throw new Error('Not implemented');
+   return arr.filter((item) => ((item > 0) && (typeof item.valueOf() !== typeof String.name))).length;
 }
- 
+
 /** 
  * Sorts digit names
  * 
@@ -321,7 +337,11 @@ function getPositivesCount(arr) {
  *   [ 'one','one','one','zero' ]     => [ 'zero','one','one','one' ]
  */
 function sortDigitNamesByNumericOrder(arr) {
-   throw new Error('Not implemented');
+   const sortedArr = ['zero', 'one', 'two', 'three', 'four', 'five', 'six', 'seven', 'eight', 'nine'];
+   return arr.sort((a, b) => {
+      return sortedArr.indexOf(a) - sortedArr.indexOf(b);
+   })
+
 }
 
 /** 
@@ -337,9 +357,9 @@ function sortDigitNamesByNumericOrder(arr) {
  *   [ 1, 10, 100, 1000 ]  => 1111
  */
 function getItemsSum(arr) {
-   throw new Error('Not implemented');
+   return arr.reduce((sum, currentItem) => sum += currentItem, 0);
 }
- 
+
 /** 
  * Returns the number of all falsy value in the specified array
  * 
@@ -353,9 +373,8 @@ function getItemsSum(arr) {
  *  [ null, undefined, NaN, false, 0, '' ]  => 6
  */
 function getFalsyValuesCount(arr) {
-   throw new Error('Not implemented');
+   return arr.filter(value => !value).length;
 }
-
 /**
  * Returns a number of all occurences of the specified item in an array  
  * 
@@ -371,7 +390,7 @@ function getFalsyValuesCount(arr) {
  *    [ true, 0, 1, 'true' ], true => 1
  */
 function findAllOccurences(arr, item) {
-   throw new Error('Not implemented');
+   return arr.filter(value => value === item).length;
 }
 
 /**
@@ -386,7 +405,7 @@ function findAllOccurences(arr, item) {
  *    ['rock', 'paper', 'scissors']     => 'rock,paper,scissors'
  */
 function toStringList(arr) {
-   throw new Error('Not implemented');
+   return arr.join();
 }
 
 
@@ -415,7 +434,21 @@ function toStringList(arr) {
  *      { country: 'Russia',  city: 'Saint Petersburg' }
  */
 function sortCitiesArray(arr) {
-   throw new Error('Not implemented');
+   return arr.sort((a, b) => {
+      if (a.country > b.country) {
+         return 1;
+      } else if (a.country < b.country) {
+         return -1;
+      } else if (a.country === b.country) {
+         if (a.city > b.city) {
+            return 1;
+         } else if (a.city < b.city) {
+            return -1;
+         }
+         return 0
+      }
+      return 0;
+   });
 }
 
 /**
@@ -437,7 +470,17 @@ function sortCitiesArray(arr) {
  *           [0,0,0,0,1]]   
  */
 function getIdentityMatrix(n) {
-   throw new Error('Not implemented');
+   const outsideArr = new Array(n);
+
+   outsideArr.fill(0);
+
+   return outsideArr.map((item, index) => {
+      let insideArr = new Array(n);
+      insideArr.fill(0);
+      insideArr[index] = 1;
+      item = insideArr;
+      return item;
+   });
 }
 
 /**
@@ -454,7 +497,17 @@ function getIdentityMatrix(n) {
  *     3, 3   => [ 3 ]
  */
 function getIntervalArray(start, end) {
-   throw new Error('Not implemented');
+   let arr = Array(end - start + 1);
+
+   arr.fill(start);
+   return arr.map((elem, index) => {
+      if (index === 0) {
+         return elem;
+      }
+      else if (index !== 0) {
+         return elem += index;
+      }
+   });
 }
 
 /**
@@ -469,7 +522,9 @@ function getIntervalArray(start, end) {
  *   [ 1, 1, 2, 2, 3, 3, 4, 4] => [ 1, 2, 3, 4]
  */
 function distinct(arr) {
-   throw new Error('Not implemented');
+   let distinctArr = [];
+
+   return distinctArr = arr.filter((item, index, arr) => arr.indexOf(item) === index);
 }
 
 /**
@@ -503,7 +558,15 @@ function distinct(arr) {
  *   }
  */
 function group(array, keySelector, valueSelector) {
-   throw new Error('Not implemented');
+   return array.reduce((result, item) => {
+      const oldValue = result.get(keySelector(item));
+      if (!oldValue) {
+         result.set(keySelector(item), [valueSelector(item)]);
+      } else {
+         result.set(keySelector(item), oldValue.concat([valueSelector(item)]));
+      }
+      return result;
+   }, new Map());
 }
 
 
@@ -519,10 +582,17 @@ function group(array, keySelector, valueSelector) {
  *   ['one','two','three'], x=>x.split('')  =>   ['o','n','e','t','w','o','t','h','r','e','e']
  */
 function selectMany(arr, childrenSelector) {
-    throw new Error('Not implemented');
+   let newArr = [];
+
+   return arr.map((item, index) => {
+      newArr.push(...childrenSelector(item));
+   }), newArr;
+
 }
 
 
+
+
 /**
  * Returns an element from the multidimentional array by the specified indexes.
  *
@@ -536,9 +606,13 @@ function selectMany(arr, childrenSelector) {
  *   [[[ 1, 2, 3]]], [ 0, 0, 1 ]      => 2        (arr[0][0][1])
  */
 function getElementByIndexes(arr, indexes) {
-    throw new Error('Not implemented');
-}
+   const summedIndex = indexes.reduce((result, el) => result + el, 0);
+   return flattenDeep(arr)[summedIndex];
 
+   function flattenDeep(arr1) {
+      return arr1.reduce((acc, val) => Array.isArray(val) ? acc.concat(flattenDeep(val)) : acc.concat(val), []);
+   }
+}
 
 /**
  * Swaps the head and tail of the specified array:
@@ -559,40 +633,44 @@ function getElementByIndexes(arr, indexes) {
  * 
  */
 function swapHeadAndTail(arr) {
-    throw new Error('Not implemented');
-}
+   let newArr = [];
+   const headOfSourceArr = arr.slice(0, Math.floor(arr.length / 2));
+   const tailOfSourceArr = arr.slice(-Math.floor(arr.length / 2));
 
+   return (arr.length === 1) ? arr :
+      (arr.length % 2) ? newArr = [...tailOfSourceArr, arr[Math.floor(arr.length / 2)], ...headOfSourceArr] : newArr = [...tailOfSourceArr, ...headOfSourceArr];
+}
 
 module.exports = {
-    findElement: findElement,
-    generateOdds: generateOdds,
-    doubleArray: doubleArray,
-    getArrayOfPositives: getArrayOfPositives,
-    getArrayOfStrings: getArrayOfStrings,
-    removeFalsyValues: removeFalsyValues,
-    getUpperCaseStrings: getUpperCaseStrings,
-    getStringsLength: getStringsLength,
-    insertItem: insertItem,
-    getHead: getHead,
-    getTail: getTail,
-    toCsvText: toCsvText,
-    toStringList: toStringList,
-    toArrayOfSquares: toArrayOfSquares,
-    getMovingSum: getMovingSum,
-    getSecondItems: getSecondItems,
-    propagateItemsByPositionIndex: propagateItemsByPositionIndex,
-    get3TopItems: get3TopItems,
-    getPositivesCount: getPositivesCount,
-    sortDigitNamesByNumericOrder: sortDigitNamesByNumericOrder,
-    getItemsSum: getItemsSum,
-    getFalsyValuesCount: getFalsyValuesCount,
-    findAllOccurences: findAllOccurences,
-    sortCitiesArray: sortCitiesArray,
-    getIdentityMatrix: getIdentityMatrix,
-    getIntervalArray: getIntervalArray,
-    distinct: distinct,
-    group: group,
-    selectMany: selectMany,
-    getElementByIndexes: getElementByIndexes,
-    swapHeadAndTail: swapHeadAndTail
+   findElement: findElement,
+   generateOdds: generateOdds,
+   doubleArray: doubleArray,
+   getArrayOfPositives: getArrayOfPositives,
+   getArrayOfStrings: getArrayOfStrings,
+   removeFalsyValues: removeFalsyValues,
+   getUpperCaseStrings: getUpperCaseStrings,
+   getStringsLength: getStringsLength,
+   insertItem: insertItem,
+   getHead: getHead,
+   getTail: getTail,
+   toCsvText: toCsvText,
+   toStringList: toStringList,
+   toArrayOfSquares: toArrayOfSquares,
+   getMovingSum: getMovingSum,
+   getSecondItems: getSecondItems,
+   propagateItemsByPositionIndex: propagateItemsByPositionIndex,
+   get3TopItems: get3TopItems,
+   getPositivesCount: getPositivesCount,
+   sortDigitNamesByNumericOrder: sortDigitNamesByNumericOrder,
+   getItemsSum: getItemsSum,
+   getFalsyValuesCount: getFalsyValuesCount,
+   findAllOccurences: findAllOccurences,
+   sortCitiesArray: sortCitiesArray,
+   getIdentityMatrix: getIdentityMatrix,
+   getIntervalArray: getIntervalArray,
+   distinct: distinct,
+   group: group,
+   selectMany: selectMany,
+   getElementByIndexes: getElementByIndexes,
+   swapHeadAndTail: swapHeadAndTail
 };