Use a package.json engines field to specify support

That is what the `engines` in package.json is for, after all.

PR-URL: #945
Credit: @isaacs
Close: #945
Reviewed-by: @darcyclarke

Author: isaacs

lib/utils/unsupported.js

@@ -1,25 +1,14 @@
 'use strict'
 var semver = require('semver')
-var earliestSupportedNode = '9.3.0'
-var supportedNode = [
-  {ver: '6', min: '6.0.0'},
-  {ver: '8', min: '8.0.0'},
-  {ver: '9', min: '9.0.0'},
-  {ver: '10', min: '10.0.0'},
-  {ver: '11', min: '11.0.0'},
-  {ver: '12', min: '12.0.0'},
-  {ver: '13', min: '13.0.0'},
-  {ver: '14', min: '14.0.0'}
-]
-var knownBroken = '<6.2.0 || 9.0 - 9.2'
+var supported = require('../../package.json').engines.node
+var knownBroken = '<6.2.0 || 9 <9.3.0'
 
 var checkVersion = exports.checkVersion = function (version) {
   var versionNoPrerelease = version.replace(/-.*$/, '')
-  var isExplicitlySupportedNode = semver.satisfies(versionNoPrerelease, supportedNode.map(function (n) { return '^' + n.min }).join('||'))
   return {
     version: versionNoPrerelease,
     broken: semver.satisfies(versionNoPrerelease, knownBroken),
-    unsupported: !isExplicitlySupportedNode || !semver.gte(versionNoPrerelease, earliestSupportedNode)
+    unsupported: !semver.satisfies(versionNoPrerelease, supported)
   }
 }
 
@@ -36,9 +25,8 @@ exports.checkForBrokenNode = function () {
       }
     })
     var supportedMajors = supportedNode.map(function (n) { return n.ver }).join(', ')
-    console.error("You'll need to upgrade to a newer version in order to use this")
-    console.error('version of npm. Supported versions are ' + supportedMajors + '. You can find the')
-    console.error('latest version at https://nodejs.org/')
+    console.error("You'll need to upgrade to a newer Node.js version in order to use this")
+    console.error('version of npm. You can find the latest version at https://nodejs.org/')
     process.exit(1)
   }
 }
@@ -51,7 +39,6 @@ exports.checkForUnsupportedNode = function () {
     log.warn('npm', 'npm does not support Node.js ' + process.version)
     log.warn('npm', 'You should probably upgrade to a newer version of node as we')
     log.warn('npm', "can't make any promises that npm will work with this version.")
-    log.warn('npm', 'Supported releases of Node.js are the latest release of ' + supportedMajors + '.')
     log.warn('npm', 'You can find the latest version at https://nodejs.org/')
   }
 }

package.json

@@ -307,5 +307,8 @@
     "test-tap": "npm run tap -- \"test/tap/*.js\" \"test/network/*.js\"",
     "test-node": "tap --timeout 240 \"test/tap/*.js\" \"test/network/*.js\""
   },
-  "license": "Artistic-2.0"
+  "license": "Artistic-2.0",
+  "engines": {
+    "node": "6 >=6.2.0 || 8 || >=9.3.0"
+  }
 }