How to Get Byte Length of String in Javascript

In this tutorial, you will learn how to get byte length of string in javascript. The byte length of a string represents the total number of bytes in that string.

There are numerous ways to get the byte length of a string. But for the sake of simplicity, we will use TextEncoder object. This object contains encode() method which takes a string as a parameter and returns Uint8Array object.

In the following example, we have one global variable that holds a string. Upon click of a button, we will get the byte length of a string and display it on the screen.  Please have a look over the code example and the steps given below.


  • We have 3 elements in the HTML file (div, button, and h1). The div element is just a wrapper for the rest of the elements.
  • The innerText for the button element is “Get” and for the h1 element, it is “Result”.
  • We have done some basic styling using CSS and added the link to our style.css stylesheet inside the head element.
  • We have also included our javascript file script.js with a script tag at the bottom.
<!DOCTYPE html>
<html lang="en">

  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <link rel="stylesheet" href="style.css">


  <div class="container">    

  <script src="script.js"></script>

.container {        
    text-align: center;

button {
  margin-top: 10px;
  padding: 10px 20px;


  • We have selected the button element and h1 element using the document.querySelector() method and stored them in btnGet and output variables respectively.
  • We have a global variable myString which holds a string as its value.
  • We have attached a click event listener to the button element.
  • In the event handler function, we are using the TextEncoder() constructor to get the TextEncoder object. We are further calling encode() method and passing myString as a parameter.
  • We are storing the returned Uint8Array in the encoded variable.
  • We are using length property to get the length of the Uint8Array. We are assigning the returned value to the result variable.
  • We are displaying the result in the h1 element using the innerText property.
let btnGet = document.querySelector("button");
let output = document.querySelector("h1");

let myString = "Hello world";

btnGet.addEventListener("click", () => {  
  let encoded = new TextEncoder().encode(myString);  
  let result = encoded.length;
  output.innerText = result;