fix(linear-progress): Add aria attributes to linear progress bar to support screen readers

packages/mdc-linear-progress/README.md

@@ -39,8 +39,9 @@ npm install @material/linear-progress
 ## Basic Usage
 
 ### HTML Structure
+
 ```html
-<div role="progressbar" class="mdc-linear-progress">
+<div role="progressbar" class="mdc-linear-progress" aria-label="Example Progress Bar" aria-valuemin="0" aria-valuemax="1" aria-valuenow="0">
   <div class="mdc-linear-progress__buffering-dots"></div>
   <div class="mdc-linear-progress__buffer"></div>
   <div class="mdc-linear-progress__bar mdc-linear-progress__primary-bar">
@@ -52,6 +53,19 @@ npm install @material/linear-progress
 </div>
 ```
 
+### Accessibility
+
+Progress bars conform to the [WAI-ARIA Progressbar Specification](https://www.w3.org/TR/wai-aria/#progressbar). The supported ARIA attributes for this progress bar are:
+
+| Attribute | Description |
+| --------- | ----------- |
+| `aria-label` | Label indicating how the progress bar should be announced to the user. |
+| `aria-valuemin` | The minimum numeric value of the progress bar, which should always be `0`. |
+| `aria-valuemax` | The maximum numeric value of the progress bar, which should always be `1`. |
+| `aria-valuenow` | A numeric value between `aria-valuemin` and `aria-valuemax` indicating the progress value of the primary progress bar. This attribute is removed in indeterminate progress bars. |
+
+Note that `aria-label`, `aria-valuemin`, and `aria-valuemax` are static and must be configured in the HTML. `aria-valuenow` is updated dynamically by the foundation when the progress value is updated in determinate progress bars.
+
 ### Styles
 ```scss
 @import "@material/linear-progress/mdc-linear-progress";
@@ -93,11 +107,13 @@ The adapter for linear progress must provide the following functions, with corre
 | Method Signature | Description |
 | --- | --- |
 | `addClass(className: string) => void` | Adds a class to the root element. |
+| `removeAttribute(attributeName: string) => void` | Removes the specified attribute from the root element. |
 | `removeClass(className: string) => void` | Removes a class from the root element. |
 | `hasClass(className: string) => boolean` | Returns boolean indicating whether the root element has a given class. |
 | `forceLayout() => void` | Force-trigger a layout on the root element. This is needed to restart animations correctly. |
 | `getPrimaryBar() => Element` | Returns the primary bar element. |
 | `getBuffer() => Element` | Returns the buffer element. |
+| `setAttribute(attributeName: string, value: string) => void` | Sets the specified attribute on the root element. |
 | `setStyle(el: Element, styleProperty: string, value: string) => void` | Sets the inline style on the given element. |
 
 ### MDCLinearProgressFoundation API

packages/mdc-linear-progress/adapter.ts

@@ -35,5 +35,7 @@ export interface MDCLinearProgressAdapter {
   getPrimaryBar(): HTMLElement | null;
   hasClass(className: string): boolean;
   removeClass(className: string): void;
+  removeAttribute(name: string): void;
+  setAttribute(name: string, value: string): void;
   setStyle(el: HTMLElement, styleProperty: string, value: string): void;
 }

packages/mdc-linear-progress/component.ts

@@ -63,7 +63,13 @@ export class MDCLinearProgress extends MDCComponent<MDCLinearProgressFoundation>
       getBuffer: () => this.root_.querySelector(MDCLinearProgressFoundation.strings.BUFFER_SELECTOR),
       getPrimaryBar: () => this.root_.querySelector(MDCLinearProgressFoundation.strings.PRIMARY_BAR_SELECTOR),
       hasClass: (className: string) => this.root_.classList.contains(className),
+      removeAttribute: (attributeName: string) => {
+        this.root_.removeAttribute(attributeName);
+      },
       removeClass: (className: string) => this.root_.classList.remove(className),
+      setAttribute: (attributeName: string, value: string) => {
+        this.root_.setAttribute(attributeName, value);
+      },
       setStyle: (el: HTMLElement, styleProperty: string, value: string) => el.style.setProperty(styleProperty, value),
     };
     return new MDCLinearProgressFoundation(adapter);

packages/mdc-linear-progress/constants.ts

@@ -28,6 +28,7 @@ export const cssClasses = {
 };
 
 export const strings = {
+  ARIA_VALUENOW: 'aria-valuenow',
   BUFFER_SELECTOR: '.mdc-linear-progress__buffer',
   PRIMARY_BAR_SELECTOR: '.mdc-linear-progress__primary-bar',
 };

packages/mdc-linear-progress/foundation.ts

@@ -42,7 +42,9 @@ export class MDCLinearProgressFoundation extends MDCFoundation<MDCLinearProgress
       getBuffer: () => null,
       getPrimaryBar: () => null,
       hasClass: () => false,
+      removeAttribute: () => undefined,
       removeClass: () => undefined,
+      setAttribute: () => undefined,
       setStyle: () => undefined,
     };
   }
@@ -68,6 +70,7 @@ export class MDCLinearProgressFoundation extends MDCFoundation<MDCLinearProgress
 
     if (this.isDeterminate_) {
       this.adapter_.removeClass(cssClasses.INDETERMINATE_CLASS);
+      this.adapter_.setAttribute(strings.ARIA_VALUENOW, this.progress_.toString());
       this.setScale_(this.adapter_.getPrimaryBar(), this.progress_);
       this.setScale_(this.adapter_.getBuffer(), this.buffer_);
     } else {
@@ -83,6 +86,7 @@ export class MDCLinearProgressFoundation extends MDCFoundation<MDCLinearProgress
       }
 
       this.adapter_.addClass(cssClasses.INDETERMINATE_CLASS);
+      this.adapter_.removeAttribute(strings.ARIA_VALUENOW);
       this.setScale_(this.adapter_.getPrimaryBar(), 1);
       this.setScale_(this.adapter_.getBuffer(), 1);
     }
@@ -92,6 +96,7 @@ export class MDCLinearProgressFoundation extends MDCFoundation<MDCLinearProgress
     this.progress_ = value;
     if (this.isDeterminate_) {
       this.setScale_(this.adapter_.getPrimaryBar(), value);
+      this.adapter_.setAttribute(strings.ARIA_VALUENOW, value.toString());
     }
   }
 

test/unit/mdc-linear-progress/foundation.test.js

@@ -28,7 +28,7 @@ import {setupFoundationTest} from '../helpers/setup';
 import {verifyDefaultAdapter} from '../helpers/foundation';
 import {MDCLinearProgressFoundation} from '../../../packages/mdc-linear-progress/foundation';
 
-const {cssClasses} = MDCLinearProgressFoundation;
+const {cssClasses, strings} = MDCLinearProgressFoundation;
 
 suite('MDCLinearProgressFoundation');
 
@@ -42,13 +42,21 @@ test('exports cssClasses', () => {
 
 test('defaultAdapter returns a complete adapter implementation', () => {
   verifyDefaultAdapter(MDCLinearProgressFoundation, [
-    'addClass', 'getPrimaryBar', 'forceLayout', 'getBuffer', 'hasClass', 'removeClass', 'setStyle',
+    'addClass',
+    'getPrimaryBar',
+    'forceLayout',
+    'getBuffer',
+    'hasClass',
+    'removeAttribute',
+    'removeClass',
+    'setAttribute',
+    'setStyle',
   ]);
 });
 
 const setupTest = () => setupFoundationTest(MDCLinearProgressFoundation);
 
-test('#setDeterminate adds class and resets transforms', () => {
+test('#setDeterminate false adds class, resets transforms, and removes aria-valuenow', () => {
   const {foundation, mockAdapter} = setupTest();
   td.when(mockAdapter.hasClass(cssClasses.INDETERMINATE_CLASS)).thenReturn(false);
   const primaryBar = {};
@@ -60,6 +68,7 @@ test('#setDeterminate adds class and resets transforms', () => {
   td.verify(mockAdapter.addClass(cssClasses.INDETERMINATE_CLASS));
   td.verify(mockAdapter.setStyle(primaryBar, 'transform', 'scaleX(1)'));
   td.verify(mockAdapter.setStyle(buffer, 'transform', 'scaleX(1)'));
+  td.verify(mockAdapter.removeAttribute(strings.ARIA_VALUENOW));
 });
 
 test('#setDeterminate removes class', () => {
@@ -87,6 +96,7 @@ test('#setDeterminate restores previous progress value after toggled from false
   foundation.setDeterminate(false);
   foundation.setDeterminate(true);
   td.verify(mockAdapter.setStyle(primaryBar, 'transform', 'scaleX(0.123)'), {times: 2});
+  td.verify(mockAdapter.setAttribute(strings.ARIA_VALUENOW, '0.123'), {times: 2});
 });
 
 test('#setDeterminate restores previous buffer value after toggled from false to true', () => {
@@ -109,16 +119,18 @@ test('#setDeterminate updates progress value set while determinate is false afte
   foundation.setProgress(0.123);
   foundation.setDeterminate(true);
   td.verify(mockAdapter.setStyle(primaryBar, 'transform', 'scaleX(0.123)'));
+  td.verify(mockAdapter.setAttribute(strings.ARIA_VALUENOW, '0.123'));
 });
 
-test('#setProgress sets transform', () => {
+test('#setProgress sets transform and aria-valuenow', () => {
   const {foundation, mockAdapter} = setupTest();
   td.when(mockAdapter.hasClass(cssClasses.INDETERMINATE_CLASS)).thenReturn(false);
   const primaryBar = {};
   td.when(mockAdapter.getPrimaryBar()).thenReturn(primaryBar);
   foundation.init();
   foundation.setProgress(0.5);
   td.verify(mockAdapter.setStyle(primaryBar, 'transform', 'scaleX(0.5)'));
+  td.verify(mockAdapter.setAttribute(strings.ARIA_VALUENOW, '0.5'));
 });
 
 test('#setProgress on indeterminate does nothing', () => {
@@ -129,6 +141,7 @@ test('#setProgress on indeterminate does nothing', () => {
   foundation.init();
   foundation.setProgress(0.5);
   td.verify(mockAdapter.setStyle(), {times: 0, ignoreExtraArgs: true});
+  td.verify(mockAdapter.setAttribute(), {times: 0, ignoreExtraArgs: true});
 });
 
 test('#setBuffer sets transform', () => {

test/unit/mdc-linear-progress/mdc-linear-progress.test.js

@@ -28,7 +28,8 @@ import {MDCLinearProgress, MDCLinearProgressFoundation} from '../../../packages/
 
 function getFixture() {
   return bel`
-    <div role="progressbar" class="mdc-linear-progress">
+    <div role="progressbar" class="mdc-linear-progress" aria-label="Unit Test Progress Bar" aria-valuemin="0"
+      aria-valuemax="1" aria-valuenow="0">
       <div class="mdc-linear-progress__buffering-dots"></div>
       <div class="mdc-linear-progress__buffer"></div>
       <div class="mdc-linear-progress__bar mdc-linear-progress__primary-bar">
@@ -58,6 +59,7 @@ test('set indeterminate', () => {
 
   component.determinate = false;
   assert.isOk(root.classList.contains('mdc-linear-progress--indeterminate'));
+  assert.equal(undefined, root.getAttribute(MDCLinearProgressFoundation.strings.ARIA_VALUENOW));
 });
 
 test('set progress', () => {
@@ -66,6 +68,7 @@ test('set progress', () => {
   component.progress = 0.5;
   const primaryBar = root.querySelector(MDCLinearProgressFoundation.strings.PRIMARY_BAR_SELECTOR);
   assert.equal('scaleX(0.5)', primaryBar.style.transform);
+  assert.equal('0.5', root.getAttribute(MDCLinearProgressFoundation.strings.ARIA_VALUENOW));
 });
 
 test('set buffer', () => {