How to Get String Size in Bytes in Javascript

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

There are numerous ways to get the string size in bytes. 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 string size in bytes 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;