March 28, 2022

How to Check if String is Valid Base64 in Javascript

By Krishnaa JavaScript Questions 0 Comments

In this tutorial, you will learn how to check if string is valid base64 in javascript. Base64 is an encoding scheme that represents binary data in ASCII string format. This makes it easy to send data over the internet via email or HTML form. Not only this but you can also convert an entire image to a base64 encoded string and use it as a source for an img tag.

There are numerous ways to check if a string is valid base64. We are going to use one of the easiest solutions which involve the usage of the match() method and ternary (?) operator. The match() method matches a string against a regular expression. If the match is found, it returns an array of matches, otherwise returns null. The ternary operator is also known as the conditional operator which acts similar to the if-else statement.

In the following example, we have one global variable and upon click of a button, we will check whether it is valid base64 or not and display the result on the screen. Please have a look over the code example and the steps given below.

HTML & CSS

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 “Check” 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">

<head>
  <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">
  <title>Document</title>
</head>

<body>

  <div class="container">    
    <button>Check</button>
    <h1>Result</h1>
  </div>

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

</html>

.container {        
    text-align: center;
}

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

Javascript

We have selected the button element and h1 element using the document.querySelector() method and stored them in btnCheck and output variables respectively.
We have attached a click event listener to the button element.
We have a global variable myVar which holds a base64 encoded string as its value.
In the event handler function, we are using match() method and ternary (?) operator to verify whether myVar is valid base64 or not. Depending upon the result of the check, we will assign “Base64” or “Not Base64” to the result variable.
We are displaying the result in the h1 element using the innerText property.

let btnCheck = document.querySelector("button");
let output = document.querySelector("h1");

let myVar = "a29kZWJhc2U=";

btnCheck.addEventListener("click", () => {
  let patttern = /^([A-Za-z0-9+/]{4})*([A-Za-z0-9+/]{3}=|[A-Za-z0-9+/]{2}==)?$/;
  let result = myVar.match(patttern) ? "Base64" : "Not Base64";
  output.innerText = result;
});

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