<mwc-textarea>
IMPORTANT: The Material Web Components are a work in progress and subject to major changes until 1.0 release.
Text areas let users enter and edit text.
Material Design Guidelines: text areas
Installation
npm install @dev.mohe/mwc-textarea
NOTE: The Material Web Components are distributed as ES2017 JavaScript Modules, and use the Custom Elements API. They are compatible with all modern browsers including Chrome, Firefox, Safari, Edge, and IE11, but an additional tooling step is required to resolve bare module specifiers, as well as transpilation and polyfills for IE11. See here for detailed instructions.
Example usage
Standard
<mwc-textarea label="My Textarea"></mwc-textarea>
<script type="module">
import '@dev.mohe/mwc-textarea';
</script>
Helper Text
<mwc-textarea label="My Textarea" helper="Helper Text"></mwc-textarea>
Primary Color
<style>
mwc-textarea {
--mdc-theme-primary: green;
}
</style>
<mwc-textarea
label="My Textarea"
required>
</mwc-textarea>
Variants
Outlined
<mwc-textarea
outlined
label="My Textarea">
</mwc-textarea>
Shaped
<style>
mwc-textarea.rounded {
--mdc-shape-small: 28px;
}
</style>
<mwc-textarea
class="rounded"
label="My Textarea"
outlined>
</mwc-textarea>
API
Properties/Attributes
Name | Type | Description |
---|---|---|
rows |
number |
Sets number of visible text lines. |
cols |
number |
Sets the visible width of the textarea. |
value |
string |
The input control's value. |
type |
TextFieldType* |
A string specifying the type of control to render. |
label |
string |
Sets floating label value. |
placeholder |
string |
Sets disappearing input placeholder. |
icon |
string |
Leading icon to display in input. See mwc-icon . |
iconTrailing |
string |
Trailing icon to display in input. See mwc-icon . |
disabled |
boolean |
Whether or not the input should be disabled. |
charCounter |
boolean |TextAreaCharCounter**
|
Note: requires maxLength to be set. Display character counter with max length. Textareas may display an "external" or "internal" charCounter . When true , textareas display an external character counter by default. |
outlined |
boolean |
Whether or not to show the material outlined variant. |
helper |
string |
Helper text to display below the input. Display default only when focused. |
helperPersistent |
boolean |
Always show the helper text despite focus. |
required |
boolean |
Displays error state if value is empty and input is blurred. |
maxLength |
number |
Maximum length input to accept. |
validationMessage |
string |
Message to show in the error color when the textarea is invalid. (Helper text will not be visible) |
validity |
ValidityState (readonly) |
The ValidityState of the textfield. |
willValidate |
boolean (readonly) |
HTMLInputElement.prototype.willValidate |
validityTransform |
ValidityTransform*** |null
|
Callback called before each validation check. See the validation section for more details. |
validateOnInitialRender |
boolean |
Runs validation check on initial render. |
name |
string |
Sets the name attribute on the internal textarea.*** |
* TextFieldType
is exported by mwc-textarea
and mwc-textarea-base
.
type TextFieldType = 'text'|'search'|'tel'|'url'|'email'|'password'|
'date'|'month'|'week'|'time'|'datetime-local'|'number'|'color';
** TextAreaCharCounter
is exported by mwc-textarea
.
type TextAreaCharCounter = 'external'|'internal';
\*\*\* `ValidityTransform` is not exported. See the [validation section](#Validation) for more details.
```ts
type ValidityTransform = (value: string, nativeValidity: ValidityState) => Partial<ValidityState>
*** The name
property should only be used for browser autofill as webcomponent form participation does not currently consider the name
attribute. See #289.
Methods
Name | Description |
---|---|
checkValidity() => boolean |
Returns true if the textarea passes validity checks. Returns false and fires an invalid event on the textarea otherwise. |
reportValidity() => boolean |
Runs checkValidity() method, and if it returns false, then it reports to the user that the input is invalid. |
setCustomValidity(message:string) => void |
Sets a custom validity message (also overwrites validationMessage ). If this message is not the empty string, then the element is suffering from a custom validity error and does not validate. |
layout() => Promise<void> |
Re-calculate layout. If a textarea is styled with display:none before it is first rendered, and it has a label that is floating, then you must call layout() the first time you remove display:none , or else the notch surrounding the label will not render correctly. |
CSS Custom Properties
Inherits CSS Custom properties from:
Name | Default | Description |
---|---|---|
--mdc-text-area-filled-border-radius |
4px 4px 0 0 |
Border radius of the standard / filled textarea's background filling. |
--mdc-text-area-outlined-idle-border-color |
rgba(0, 0, 0, 0.38) |
Color of the outlined textarea's outline when idle. |
--mdc-text-area-outlined-hover-border-color |
rgba(0, 0, 0, 0.87) |
Color of the outlined textarea's outline when hovering. |
--mdc-text-area-outlined-disabled-border-color |
rgba(0, 0, 0, 0.06) |
Color of the outlined textarea's outline when disabled. |
Global Custom Properties
This component exposes the following global theming custom properties.
Name | Description |
---|---|
--mdc-theme-primary |
Color when active of the underline ripple, the outline, and the caret. |
--mdc-theme-error |
Color when errored of the underline, the outline, the caret, and the icons. |
--mdc-typography-subtitle1-<PROPERTY> |
Styles the typography of the texarea, excluding line-height. |
Validation
<mwc-textarea>
follows the basic <input>
constraint validation model.
It exposes:
required
maxLength
validity
willValidate
checkValidity()
reportValidity()
setCustomValidity(message)
Additionally, it implements more features such as:
validationMessage
validateOnInitialRender
- and
validityTransform
By default, <mwc-textarea>
will report validation on blur
.
Custom validation logic
The validityTransform
property is a function that can be set on <mwc-textarea>
to
implement custom validation logic that transforms the ValidityState
of the
input control. The type of a ValidityTransform
is the following:
(value: string, nativeValidity: ValidityState) => Partial<ValidityState>
Where value
is the new value in the textarea to be validated and
nativeValidity
is an interface of
ValidityState
of the native input control. For example:
<mwc-textarea
id="my-textarea"
maxlength="5"
value="doggos">
</mwc-textarea>
<script>
const textarea = document.querySelector('#my-textarea');
textarea.validityTransform = (newValue, nativeValidity) => {
if (!nativeValidity.valid) {
if (nativeValidity.tooLong) {
const hasDog = newValue.includes('dog');
// changes to make to the nativeValidity
return {
valid: hasDog,
tooLong: !hasDog;
};
} else {
// no changes
return {};
}
} else {
const isValid = someExpensiveOperation(newValue);
// changes to make to the native validity
return {
valid: isValid,
// or whatever type of ValidityState prop you would like to set (if any)
customError: !isValid,
};
}
}
</script>
In this example we first check the native validity which is invalid due to the
maxlength (the value is doggos
which is a string longer than 5). The value
includes dog
, thus we make it valid and undo the tooLong
error in the
ValidityState
by returning a Partial<ValidityState>
that indicates what to
change in the initial validity.
In this example, we also skip an expensive validity check by short-circuiting the validation by checking the native validation.
Note: the UI will only update as valid / invalid by checking the valid
property of the transformed ValidityState
.