feat(textfield): helperTextContent setter

packages/mdc-textfield/README.md

@@ -373,6 +373,10 @@ being used as the text field's "helper text". It defaults to `null`. If the text
 contains an `aria-controls` attribute on instantiation of the component, it will look for an element
 with the corresponding id within the document and automatically assign it to this property.
 
+##### MDCTextField.helperTextContent
+
+String setter. Proxies to the foundation's `setHelperTextContent` method when set.
+
 ##### MDCTextField.disabled
 
 Boolean. Proxies to the foundation's `isDisabled/setDisabled` methods when retrieved/set
@@ -413,6 +417,7 @@ complicated.
 | deregisterBottomLineEventHandler(evtType: string, handler: EventListener) => void | Deregisters an event listener on the bottom line element for a given event |
 | setHelperTextAttr(name: string, value: string) => void | Sets an attribute with a given value on the helper text element |
 | removeHelperTextAttr(name: string) => void | Removes an attribute from the helper text element |
+| setHelperTextContent(content: string) => void | Sets the content of the helper text element |
 | getNativeInput() => {value: string, disabled: boolean, badInput: boolean, checkValidity: () => boolean}? | Returns an object representing the native text input element, with a similar API shape. The object returned should include the `value`, `disabled` and `badInput` properties, as well as the `checkValidity()` function. We _never_ alter the value within our code, however we _do_ update the disabled property, so if you choose to duck-type the return value for this method in your implementation it's important to keep this in mind. Also note that this method can return null, which the foundation will handle gracefully. |
 | getBottomLineFoundation() => MDCTextFieldBottomLineFoundation | Returns the instance of the bottom line element's foundation |
 

packages/mdc-textfield/adapter.js

@@ -164,6 +164,12 @@ class MDCTextFieldAdapter {
    */
   removeHelperTextAttr(name) {}
 
+  /**
+   * Sets the text content for the help text element
+   * @param {string} content
+   */
+  setHelperTextContent(content) {}
+
   /**
    * Returns an object representing the native text input element, with a
    * similar API shape. The object returned should include the value, disabled

packages/mdc-textfield/foundation.js

@@ -61,6 +61,7 @@ class MDCTextFieldFoundation extends MDCFoundation {
       deregisterBottomLineEventHandler: () => {},
       setHelperTextAttr: () => {},
       removeHelperTextAttr: () => {},
+      setHelperTextContent: () => {},
       getNativeInput: () => {},
       getBottomLineFoundation: () => {},
     });
@@ -311,6 +312,13 @@ class MDCTextFieldFoundation extends MDCFoundation {
     }
   }
 
+  /**
+   * @param {string} content Sets the content of the helper text field
+   */
+  setHelperTextContent(content) {
+    this.adapter_.setHelperTextContent(content);
+  }
+
   /**
    * @return {!Element|!NativeInputType} The native text input from the
    * host environment, or a dummy if none exists.

packages/mdc-textfield/index.js

@@ -124,6 +124,13 @@ class MDCTextField extends MDCComponent {
     this.foundation_.setValid(valid);
   }
 
+  /**
+   * @param {string} content Sets the Helper Text element textContent.
+   */
+  set helperTextContent(content) {
+    this.foundation_.setHelperTextContent(content);
+  }
+
   /**
    * @return {!MDCTextFieldFoundation}
    */
@@ -236,6 +243,11 @@ class MDCTextField extends MDCComponent {
           this.helperTextElement.removeAttribute(name);
         }
       },
+      setHelperTextContent: (content) => {
+        if (this.helperTextElement) {
+          this.helperTextElement.textContent = content;
+        }
+      },
     };
   }
 }

test/unit/mdc-textfield/foundation.test.js

@@ -43,6 +43,7 @@ test('defaultAdapter returns a complete adapter implementation', () => {
     'registerInputInteractionHandler', 'deregisterInputInteractionHandler',
     'registerBottomLineEventHandler', 'deregisterBottomLineEventHandler',
     'setHelperTextAttr', 'removeHelperTextAttr', 'getNativeInput', 'getBottomLineFoundation',
+    'setHelperTextContent',
   ]);
 });
 
@@ -181,6 +182,12 @@ test('#init does not add mdc-text-field__label--float-above class if the input d
   td.verify(mockAdapter.addClassToLabel(cssClasses.LABEL_FLOAT_ABOVE), {times: 0});
 });
 
+test('#setHelperTextContent sets the content of the helper text element', () => {
+  const {foundation, mockAdapter} = setupTest();
+  foundation.setHelperTextContent('foo');
+  td.verify(mockAdapter.setHelperTextContent('foo'));
+});
+
 test('on input focuses if input event occurs without any other events', () => {
   const {foundation, mockAdapter} = setupTest();
   let input;

test/unit/mdc-textfield/mdc-text-field.test.js

@@ -138,6 +138,21 @@ test('set valid updates the component styles', () => {
   assert.isNotOk(root.classList.contains(cssClasses.INVALID));
 });
 
+test('set helperTextContent updates the helper text element content', () => {
+  const {component} = setupTest();
+  const helptext = getHelperText();
+  component.helperTextElement = helptext;
+  component.helperTextContent = 'foo';
+  assert.equal(helptext.textContent, 'foo');
+});
+
+test('set helperTextContent has no effect when no helper text element is present', () => {
+  const {component} = setupTest();
+  assert.isNull(component.helperTextElement);
+  component.helperTextContent = 'foo';
+  assert.isNull(component.helperTextElement);
+});
+
 test('#adapter.setIconAttr sets a given attribute to a given value to the icon element', () => {
   const {icon, component} = setupTest();
 
@@ -311,6 +326,19 @@ test('#adapter.removeHelperTextAttr removes an attribute on the helper text elem
   assert.isNotOk(helperText.hasAttribute('aria-label'));
 });
 
+test('#adapter.setHelperTextContent does nothing if no help text element present', () => {
+  const {component} = setupTest();
+  assert.doesNotThrow(() => component.getDefaultFoundation().adapter_.setHelperTextContent('foo'));
+});
+
+test('#adapter.setHelperTextContent updates the text content of the help text element', () => {
+  const {component} = setupTest();
+  const helptext = getHelperText();
+  component.helperTextElement = helptext;
+  component.getDefaultFoundation().adapter_.setHelperTextContent('foo');
+  assert.equal(helptext.textContent, 'foo');
+});
+
 test(`#adapter.notifyIconAction emits ${strings.ICON_EVENT}`, () => {
   const {component} = setupTest();
   const handler = td.func('leadingHandler');