March 26, 2022

How to Check if a String is a Valid URL in Javascript

By Krishnaa JavaScript Questions 0 Comments

In this tutorial, you will learn how to check if a string is a valid URL in javascript. A URL is just a unique address of a resource on the web. URL stands for Uniform Resource Locator.

There are numerous ways to check if a string is valid URL. We are going to use one of the easiest solutions which involve the usage of the try-catch block, URL interface, and ternary (?) operator. The ternary operator is also known as the conditional operator which acts similar to the if-else statement. In the try block, we run a code that is going to be tested for errors. In the catch block, we execute a certain piece of code after an error is thrown.

The URL interface plays an important in parsing and constructing URLs. You just need to provide a valid absolute or relative URL to the URL() constructor to get a URL object. The URL object exposes a bunch of helpful methods and properties which makes it extremely easy to work with any sort of URL.

In the following example, upon click of a button, we will check if a string is valid URL 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>
        <button>Check</button>
        <h1>Result</h1>
    </div>

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

body {
    text-align: center;
}

div {
    display: inline-block;
}

button {
    display: inline-block;
    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 a global variable myVar which holds a URL string as its value.

We have attached a click event listener to the button element.
In the event handler function, we are calling isValidUrl() method and passing myVar as a parameter.
In the isValidUrl() method, we have url variable which is undefined initially. In the try block, we are passing url to the URL() constructor to get a URL object. If url is valid URL, we will never enter into the catch block but if it is not, then we will get an error. Further, we are checking for http or https protocol and returning true or false.

We are using the ternary operator to check whether isValidUrl returns true or false. Depending upon the result of the check, we will assign “Yes” or “No“ 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 = "https://www.example.com";

btnCheck.addEventListener("click", () => { 
  
  let result = isValidUrl(myVar) ? "Yes" : "No";
  output.innerText = result;
  
});

function isValidUrl(str) {
  let url;  
  try {
    url = new URL(str);
  } catch (_) {
    return false;  
  }
  return url.protocol === "http:" || url.protocol === "https:";
}

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