JavaScript replace() method is used for manipulating strings. It allows you to search for a specific part of a string, called a substring, and then replace it with another substring.

What’s great is that this method doesn’t alter the original string, making it ideal for tasks where you want to maintain the integrity of the original data. Understanding how to use replace() can enhance your ability to work with strings effectively in JavaScript.

Syntax: 

str.replace(value1, value2);

Parameters:

• value1: is the regular expression that is to be replaced
• value2: is a string that will replace the content of the given string. 

Return Values:

It returns a new string with replaced items.

Example 1: Below is an example of the string.replace() Method. 

let string = 'GeeksForGeeks';
let newstring = string.replace('GeeksForGeeks', 'GfG');
console.log(newstring); 

GfG

Explanation:

• A string string is assigned the value 'GeeksForGeeks'.
• The replace() method is called on string, searching for the substring 'GeeksForGeeks' and replacing it with 'GfG'.
• Since the entire string 'GeeksForGeeks' matches, it is replaced with 'GfG'.
• The new string 'GfG' is assigned to the variable newstring.
• newstring is logged to the console.

Example 2: Here the contents of the string GeeksForGeeks will be replaced with gfg. 

 // Assigning a string
 let string = 'GeeksForGeeks is a CS portal';
    
 // Calling replace() method
 let newstring = string.replace(/GeeksForGeeks/, 'gfg');
 
 // Printing replaced string
 console.log(newstring);  

gfg is a CS portal

Explanation:

• A string string is assigned the value 'GeeksForGeeks is a CS portal'.
• The replace() method is called on string, using a regular expression to match the substring 'GeeksForGeeks' and replace it with 'gfg'.
• The first occurrence of 'GeeksForGeeks' in the string is replaced with 'gfg'.
• The modified string is assigned to the variable newstring.
• The replaced string newstring is logged to the console.

Example 3: Below is an example of the string.replace() Method. 

// Taking a regular expression
let re = /GeeksForGeeks/;

// Taking a string as input
let string = 'GeeksForGeeks is a CS portal';

// Calling replace() method to replace
// GeeksForGeeks from string with gfg
let newstring = string.replace(re, 'gfg');

// Printing new string with replaced items
console.log(newstring);

gfg is a CS portal

Explanation:

A regular expression re is defined to match the substring 'GeeksForGeeks'.

• A string string is assigned the value 'GeeksForGeeks is a CS portal'.
• The replace() method is called on string, using the regular expression re to match the substring 'GeeksForGeeks' and replace it with 'gfg'.
• The first occurrence of 'GeeksForGeeks' in the string is replaced with 'gfg'.
• The modified string is assigned to the variable newstring.
• The replaced string newstring is logged to the console.

We can also replace the same words at multiple places in a string. It is known as a global replacement.

Example 4: This example explains replacing of various similar words in a string.

// Assigning a string
let string = 'GeeksForGeeks is a CS portal.' +
    'In GeeksForGeeks we can learn multiple languages.' +
    'geeksForGeeks is a great place.';

// Calling replace() method
let newstring = string.replace(/GeeksForGeeks/g, 'Gfg');

// Printing replaced string
console.log(newstring);

Gfg is a CS portal.In Gfg we can learn multiple languages.geeksForGeeks is a great place.

Explanation:

A multi-line string string is assigned with multiple occurrences of the substring 'GeeksForGeeks'.

• The replace() method is called on string, using a regular expression with the global flag (/g) to match all occurrences of the substring 'GeeksForGeeks' case-sensitively and replacing them with 'Gfg'.
• All occurrences of 'GeeksForGeeks' in the string are replaced with 'Gfg'.
• The modified string is assigned to the variable newstring.
• The replaced string newstring is logged to the console.

Supported Browsers: 

• Google Chrome 1 and above
• Edge 12 and above
• Firefox 1 and above
• Opera 4 and above
• Safari 1 and above