Replace special characters in a string with underscore (_) in JavaScript

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In this article, we will see how to replace special characters in a string with an underscore in JavaScript. JavaScript replace() method is used to replace all special characters from a string with _ (underscore) which is described below:

JavaScript replace() Method: This method searches a string for a defined value, or a regular expression, and returns a new string with the replaced defined value.

Syntax:

string.replace(searchVal, newvalue)

Parameters:

searchVal: It is a required parameter. It specifies the value or regular expression, that is going to replace by the new value.
newvalue: It is a required parameter. It specifies the value to replace the search value with.

Return value: It returns a new string that matches the pattern specified in the parameters.

Example 1: This example replaces all special characters with _ (underscore) using replace() method.

Javascript

let str = "This, is# GeeksForGeeks!";
 
console.log(str.replace(/[&\/\\#, +()$~%.'":*?<>{}]/g, '_'));

Output

This__is__GeeksForGeeks!

Example 2: This example replaces a unique special character with _ (underscore). This example goes to each character and checks if it is a special character that we are looking for, then it will replace the character. In this example, the unique character is $(dollar sign).

Javascript

let str = "A$computer$science$portal$for$Geeks";
 
function gfg_Run() {
 
    let newStr = "";
 
    for (let i = 0; i < str.length; i++) {
        if (str[i] == '$') {
            newStr += '_';
        }
        else {
            newStr += str[i];
        }
    }
    console.log(newStr);
}        
 
gfg_Run();

Output

A_computer_science_portal_for_Geeks

Example 3: In this example, we replace a unique special character with _ (underscore). This example spread function is used to form an array from a string and form a string with the help of reduce which excludes all special character and add underscore in their places. In this example the unique character are `&\/#, +()$~%.’”:*?<>{}`.

Javascript

let check = chr => `&\/#, +()$~%.'":*?<>{}`.includes(chr);
 
let str = "This, is# GeeksForGeeks!";
 
let underscore_str = [...str]
    .reduce((s, c) => check(c) ? s + '_' : s + c, '');
 
console.log(underscore_str);