Material Components for the Web


Auto Init

mdc-auto-init is a utility package that provides declarative, DOM-based method of initialization for MDC-Web components on simple web sites. Note that for more advanced use-cases and complex sites, manual instantiation of components will give you more flexibility. However, mdc-auto-init is great for static websites, prototypes, and other use-cases where simplicity and convenience is most appropriate.


npm install --save @material/auto-init


Using as part of material-components-web

If you are using mdc-auto-init as part of the material-components-web package, simply write the necessary DOM needed for a component, and attach a data-mdc-auto-init attribute to the root element with its value set to the Component’s class name. Then, after writing the markup, simply insert a script tag that calls mdc.autoInit(). Make sure you call mdc.autoInit() after all scripts are loaded so it works properly.

<div class="mdc-textfield" data-mdc-auto-init="MDCTextfield">
  <input class="mdc-textfield__input" type="text" id="input">
  <label for="input" class="mdc-textfield__label">Input Label</label>

<!-- at the bottom of the page -->
<script type="text/javascript">

This will attach an MDCTextfield instance to the root <div> element.

Accessing the component instance

When mdc-auto-init attaches a component to an element, it assign that instance to the element using a property whose name is the value of data-mdc-auto-init. For example, given

<div class="mdc-textfield" data-mdc-auto-init="MDCTextfield">
  <input class="mdc-textfield__input" type="text" id="input">
  <label for="input" class="mdc-textfield__label">Input Label</label>

Once mdc.autoInit() is called, you can access the component instance via an MDCTextfield property on that element.

document.querySelector('.mdc-textfield').MDCTextfield.disabled = true;

Using as a standalone module

Registering Components

If you are using mdc-auto-init outside of material-components-web, you must manually provide a mapping between data-mdc-auto-init attribute values and the components which they map to. This can be achieved via mdcAutoInit.register.

import mdcAutoInit from 'mdc-auto-init';
import {MDCTextfield} from 'mdc-textfield';

mdcAutoInit.register('MDCTextfield', MDCTextfield);

mdcAutoInit.register() tells mdc-auto-init that when it comes across an element with a data-mdc-auto-init attribute set to "MDCTextfield", it should initialize an MDCTextfield instance on that element. The material-components-web package does this for all components for convenience.

Also note that a component can be mapped to any string, not necessarily the name of its constructor.

import mdcAutoInit from 'mdc-auto-init';
import {MDCTextfield} from 'mdc-textfield';

mdcAutoInit.register('My amazing text field!!!', MDCTextfield);
<div class="mdc-textfield" data-mdc-auto-init="My amazing text field!!!">
  <!-- ... -->

De-registering components

Any component can be deregistered by calling mdcAutoInit.deregister with the name used to register the component.


This will simply remove the name -> component mapping. It will not affect any already-instantiated components on the page.

To unregister all name -> component mappings, you can use mdcAutoInit.deregisterAll().

How mdc-auto-init works

mdc-auto-init maintains a registry object which maps string identifiers, or names, to component constructors. When the default exported function - mdcAutoInit() - is called, mdc-auto-init queries the DOM for all elements with a data-mdc-auto-init attribute. For each element returned, the following steps are taken:

  1. If the data-mdc-auto-init attribute does not have a value associated with it, throw an error
  2. If the value of data-mdc-auto-init cannot be found in the registry, throw an error
  3. If the element has an existing property whose name is the value of data-mdc-auto-init, it is assumed to have already been initialized. Therefore it is skipped, and a warning will be logged to the console (this behavior can be overridden).
  4. Let Ctor be the component constructor associated with the given name in the register
  5. Let instance be the result of calling Ctor.attachTo() and passing in the element as an argument.
  6. Create a non-writable, non-enumerable property on the node whose name is the value of data-mdc-auto-init and whose value is instance.

Initializing only a certain part of the page

By default, mdc-auto-init will query the entire document to figure out which components to initialize. To override this behavior, you can pass in an optional root first argument specifying the root node whose children will be queried for instantiation.

<div id="mdc-section">
  <!-- MDC-Web Components, etc. -->

In the above example, only elements within <div id="mdc-section"> will be queried.

Calling autoInit() multiple times

By default, mdc-auto-init only expects to be called once, at page-load time. However, there may be certain scenarios where one may want to use mdc-auto-init and may still need to call it multiple times, such as on a Wordpress site that contains an infinitely-scrolling list of new blog post elements containing MDC-Web components. mdcAutoInit() takes an optional second argument which is the function used to warn users when a component is initialized multiple times. By default, this is just console.warn(). However, to skip over already-initialized components without logging a warning, you could simply pass in a nop.

<script>window.mdc.autoInit(/* root */ document, () => {});</script>

This will suppress any warnings about already initialized elements.