ES6 - replace()

This method finds a match between a regular expression and a string, and replaces the matched substring with a new substring.

The replacement string can include the following special replacement patterns −

Sr.No	Patterns & Inserts
1	$$ Inserts a "$".
2	$& Inserts the matched substring.
3	$` Inserts the portion of the string that precedes the matched substring.
4	$' Inserts the portion of the string that follows the matched substring.
5	$n or $nn Where n or nn are decimal digits, inserts the nth parenthesized submatch string, provided the first argument was a RegExp object.

Syntax

string.replace(regexp/substr, newSubStr/function[, flags]);

regexp − A RegExp object. The match is replaced by the return value of parameter #2.
substr − A String that is to be replaced by newSubStr.
newSubStr − The String that replaces the substring received from parameter #1.
function − A function to be invoked to create the new substring.
flags − A String containing any combination of the RegExp flags: g.

It simply returns a new changed string.

var re = /apples/gi; 
var str = "Apples are round, and apples are juicy."; 
var newstr = str.replace(re, "oranges"); 
console.log(newstr)

oranges are round, and oranges are juicy.

var re = /(\w+)\s(\w+)/; 
var str = "zara ali"; 
var newstr = str.replace(re, "$2, $1"); 
console.log(newstr);

ali, zara