Find and replace

To search for a string inside a string, there are several functions:

indexOf( searchString ) and lastIndexOf( searchString )

indexOf() will return the index of the first occurrence of searchString in the string. If searchString is not found, then -1 is returned.

var string = "Hello, World!";
console.log( string.indexOf("o") ); // 4
console.log( string.indexOf("foo") ); // -1

Similarly, lastIndexOf() will return the index of the last occurrence of searchstring or -1 if not found.

var string = "Hello, World!";
console.log( string.lastIndexOf("o") );   // 8
console.log( string.lastIndexOf("foo") ); // -1

includes( searchString, start )

includes() will return a boolean that tells whether searchString exists in the string, starting from index start (defaults to 0). This is better than indexOf() if you simply need to test for existence of a substring.

var string = "Hello, World!";
console.log( string.includes("Hello") ); // true
console.log( string.includes("foo") );   // false

replace( regexp|substring, replacement|replaceFunction )

replace() will return a string that has all occurrences of substrings matching the RegExp regexp or string substring with a string replacement or the returned value of replaceFunction.

Note that this does not modify the string in place, but returns the string with replacements.

var string = "Hello, World!";
string = string.replace( "Hello", "Bye" );
console.log( string ); // "Bye, World!"

string = string.replace( /W.{3}d/g, "Universe" );
console.log( string ); // "Bye, Universe!"

replaceFunction can be used for conditional replacements for regular expression objects (i.e., with use with regexp). The parameters are in the following order:

Note that all parameters are optional.

var string = "heLlo, woRlD!";
string = string.replace( /([a-zA-Z])([a-zA-Z]+)/g, function(match, g1, g2) {
    return g1.toUpperCase() + g2.toLowerCase();
}); 
console.log( string ); // "Hello, World!"