JavaScript Check whether a URL string is absolute or relative

In this article, the task is to check if the passed URL is absolute or relative. Below are a few approaches: 

Approaches to Check if URL is Absolute or Relative:

• using JavaScript Regular Expression
• using JavaScript string.indexof() method

Approach 1: Using JavaScript Regular Expression

Use Regular Expression which checks if the URL contains “//” at a position in the URL.

Example: This example uses the approach discussed above.

Javascript

// Input url
let URL = "https://geeksforgeeks.org";

// Display input url
console.log(URL);

// Function to check url
function gfg_Run() {
    // Regular Expression to check url
    let RgExp = new RegExp("^(?:[a-z]+:)?//", "i");
    if (RgExp.test(URL)) {
        console.log("This is Absolute URL.");
    } else {
        console.log("This is Relative URL.");
    }
}

// Function call
gfg_Run();

Output

https://geeksforgeeks.org
This is Absolute URL.

Approach 2: Using JavaScript string.indexof() method

Use .indexOf() method to get to know if the position of “://” has an index greater than 0 or if the position of “//” has an index equal to 0. Both these conditions check to lead us to the absolute URL.

Example: This example uses the approach discussed above.

Javascript

// Input url
let URL = "/myfolder/test.txt";

// Display input url
console.log(URL);

// Function to check url type
function gfg_Run() {
    // Using index of to check url format
    if (URL.indexOf("://") > 0 || URL.indexOf("//") === 0) {
        console.log("This is Absolute URL.");
    } else {
        console.log("This is Relative URL.");
    }
}

// Function call
gfg_Run();

Output

/myfolder/test.txt
This is Relative URL.