An element that couns number of bytes in string or object

Usage no npm install needed!

<script type="module">
  import advancedRestClientBytesCounter from 'https://cdn.skypack.dev/@advanced-rest-client/bytes-counter';


Published on NPM

Build Status

Published on webcomponents.org

An element that computes number of bytes in String, ArrayBuffer, Blob (and therefore File) and - in supported browsers - from FormData.

Note that Safari is excluded from FormData tests because there's some bug in WebKit implementation of the Request object and it doesn't read FormData properly. Chrome had similar bug but they fixed it already. See demo page to check if your browser support FormData.

This element is native web component without using any library. Do not set attributes as this element do not observe changes to any. Use templating system of your choice to set a property on the element or use it imperatively.


In a Polymer template

<textarea value="{{value::input}}"></textarea>
<bytes-counter value="[[value]]" bytes="{{bytes}}"></bytes-counter>

In a LitElement template

import { LitElement, html } from 'lit-element';
import '@advanced-rest-client/bytes-counter/bytes-counter.js';

class SampleElement extends LitElement {
  render() {
    return html`
    <textarea @input="${this._inputHandler}"></textarea>
    <bytes-counter .value="${this.value}" @change="${this._computeHandler}"></bytes-counter>

  _inputHandler(e) {
    const { value } = e.target;
    this.value = value;

  _computeHandler(e) {
    const { value } = e.detail;
    console.log(`Computed input size is ${value} bytes`);
customElements.define('sample-element', SampleElement);

Imperative use

<textarea id="i1"></textarea>
<bytes-counter id="b1"></bytes-counter>
<output id="o1"></output>
  document.getElementById('i1').addEventListener('input', (e) => {
    const { value } = e.target;
    document.getElementById('b1').value = value;
  document.getElementById('b1').addEventListener('bytes-changed', (e) => {
    const { value } = e.detail;
    document.getElementById('o1').value = `Current input has ${value} bytes`;

Note that computations are asynchronous and there is a delay between setting the value property and getting a result.

New in version 3

  • Dropped support for Polymer library. It is not plain web component.
  • Added aria-hidden attribute
  • Added debouncer when setting the value
  • Deprecating bytes-changed event. Use change event instead. This event is kept for compatibility with Polymer.


git clone https://github.com/@advanced-rest-client/bytes-counter
cd bytes-counter
npm install

Running the demo locally

npm start

Running the tests

npm test