Replace all Occurrences of a Substring in a String in JavaScript

In Javascript, a string is a sequence of characters represented with quotation marks. We are given a string and we need to replace all occurrences of a substring from the given string.

Using the replace() method with regular expression

• First, declare a string variable str with the value “GeeksforGEEKS”.
• Now, declare a substring variable with the value “GEEKS” to search for and replace.
• Use the replace method with a regular expression to globally replace all instances of the substring with the replacement value “geeks”.
• It logs the result which will be “Geeks For geeks “.

Example: The below code will explain the use of replace() method with regular expression.

Javascript

let str = "GeeksforGEEKS";
let substring = "GEEKS";
let replacement = "Geeks";
console.log("Before replacement: ", str)
let finalResult =
    str.replace(new RegExp(substring, "g"),
        replacement);

console.log("After Replacement: ", finalResult);

Output

Before replacement:  GeeksforGEEKS
After Replacement:  GeeksforGeeks

Using indexOf() and slice() methods

• The indexOf() method finds the index of the first occurrence of the substring.
• If the index is greater than or equal to 0 (found a match), it slices the string before and after the match and inserts the replacement.
• It recursively calls itself to keep replacing all other matches.
• It returns the final string after replacing all matches.

Example: The below code will explain the use of the indexOf() and slice() methods to replace all occurences of a substring.

Javascript

function replaceAll(str, substring, replacement) {
    let index = str.indexOf(substring);
    if (index >= 0) {
        str =
            str.slice(0, index) + replacement +
            str.slice(index + substring.length);
        str = replaceAll(str, substring, replacement);
    }
    return str;
}
const str = "GeeksforGEEKS";
const subStr = "GEEKS";
const replacement = "Geeks";
console.log("Before replacement: ", str)
let finalResult =
    replaceAll(str, subStr, replacement);
console.log("After Replacement: ", finalResult);

Output

Before replacement:  GeeksforGEEKS
After Replacement:  GeeksforGeeks

Using replaceAll() method

• Declare a constant str variable with the initial string “GeeksforGEEKS”.
• Now, use the String.replaceAll() method to replace all occurrences of “GEEKS” in the str with “Geeks”, assigning the result to finalResult and logging it to the console.

Example: The below code is practical implementation of the above-discussed approach.

Javascript

const str = "GeeksforGEEKS";
const finalResult =
    str.replaceAll("GEEKS", "Geeks");
console.log("Before replacement: ", str)
console.log("After Replacement: ", finalResult);

Output

Before replacement:  GeeksforGEEKS
After Replacement:  GeeksforGeeks