JavaScript String.prototype.replace() - Replace Explained with Examples

Guide
1

The replace() method returns a new string with some or all matches of a pattern replaced by a replacement. The pattern can be a string or a RegExp, and the replacement can be a string or a function to be called for each match.

Syntax

str.replace(regexp|substr, newSubStr|function[, flags])

Parameters

regexp (pattern)

A RegExp object. The match is replaced by the return value of parameter #2.

substr (pattern)

A String that is to be replaced by newSubStr.

newSubStr (replacement)

The String that replaces the substring received from parameter #1. A number of special replacement patterns are supported; see the “Specifying a string as a parameter” section below.

function (replacement)

A function to be invoked to create the new substring (to put in place of the substring received from parameter #1). The arguments supplied to this function are described in the “Specifying a function as a parameter” section below.

MDN link | MSDN link

Returns

A new string with some or all matches of a pattern replaced by a replacement.

Description

This method does not change the String object it is called on. It simply returns a new string.

To perform a global search and replace, either include the g switch in the regular expression or if the first parameter is a string, include g in the flags parameter.

Examples

var str = 'Twas the night before Xmas...';
var newstr = str.replace(/xmas/i, 'Christmas');
console.log(newstr);  // Twas the night before Christmas...

function f2c(s1) {
    // Initialize pattern.
    var test = /(\d+(\.\d*)?)F\b/g;

    // Use a function for the replacement.
    var s2 = s1.replace(test,
      function($0,$1,$2)
           { 
           return((($1-32) * 5/9) + "C");
           }
        )
    return s2;
}
document.write(f2c("Water freezes at 32F and boils at 212F."));

// Output: Water freezes at 0C and boils at 100C.
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