The Polymer library provides a set of features for creating custom elements. These features are designed to make it easier and faster to make custom elements that work like standard DOM elements. Similar to standard DOM elements, Polymer elements can be:

• Instantiated using a constructor or document.createElement.
• Configured using attributes or properties.
• Populated with internal DOM inside each instance.
• Responsive to property and attribute changes (for example, by populating data into the DOM, or firing an event).
• Styled with internal defaults or externally.
• Responsive to methods that manipulate its internal state.

A basic Polymer element definition looks like this:

<dom-module id="element-name">

  <template>
    <style>
      /* CSS rules for your element */
    </style>
  
    <!-- local DOM for your element -->

    <div>{{greeting}}</div> <!-- data bindings in local DOM -->
  </template>

  <script>
    // element registration
    Polymer({
      is: "element-name",

      // add properties and methods on the element's prototype

      properties: {
        // declare properties for the element's public API
        greeting: {
          type: String,
          value: "Hello!"
        }
      }
    });
  </script>

</dom-module>

This guide divides the features into the following groups:

• Registration and lifecycle. Registering an element associates a class (prototype) with a custom element name. The element provides callbacks to manage its lifecycle. Use behaviors to share code.

• Declared properties. Declared properties can be configured from markup using attributes. Declared properties can optionally support change observers, two-way data binding, and reflection to attributes. You can also declare computed properties and read-only properties.

• Local DOM. Local DOM is the DOM created and managed by the element.

• Events. Attaching event listeners to the host object and local DOM children. Event retargeting.

• Data binding. Property bindings. Binding to attributes.

• Behaviors. Behaviors are reusable modules of code that can be mixed into Polymer elements.

• Utility functions. Helper methods for common tasks.

• Experimental features and elements. Experimental template and styling features. Feature layering.

If you’re migrating an existing 0.5 element to the new APIs, see the Migration guide for advice.

If you’re upgrading from the 0.8 release, see the Release notes.