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HTML

              
                # Auto Resize a `<textarea>` By Extending Custom Elements

First, a regular `<textarea>`.

<textarea>Will NOT auto resize.</textarea>

Now, [use the `is` attribute in HTML](https://t.co/4d2Sb8ihh0?amp=1) in combintation with web component technology so that the `<textarea>` auto resizes on input (this requires [a polyfill](https://github.com/ungap/custom-elements-builtin) to work in Safari).

<textarea is="auto-size">Will auto resize.</textarea>

Leveraging a `<textarea>` as a child means things fail gracefully if JavaScript isn’t present. Plus, you can still use the inner `<textarea>` to attach any attributes that are supported natively in HTML.


<textarea is="auto-size" rows="5" onclick="console.log('this fired')">Default value here with the attribute `rows="5" and an `onclick` event handler.</textarea>
              
            
!

CSS

              
                textarea {
  display: block;
  margin: 20px 0;
  width: 400px;
}
              
            
!

JS

              
                import autosize from "https://unpkg.com/autosize@4.0.2/src/autosize.js";

class AutoSize extends HTMLTextAreaElement {
  constructor() {
    super();
    autosize(this);
  }
}
    
customElements.define(
  "auto-size",
  AutoSize,
  { extends: "textarea" }
);

              
            
!
999px

Console