Dive Into JavaScript

The JavaScript String Object

The string data type is a primitive data type that represents a sequence of characters.

JavaScript provides both a string primitive and a global String object. The String object essentially wraps the primitive string with methods and properties used to access and manipulate individual characters or the entire string.

String Syntax

String objects can be created by calling the new String() constructor or the String() global function:

var string1 = new String([string]);

var string1 = String([string]);

String primitives can be created using the string literal form:

var string2 = 'string';

var string3 = "string";

Conversion between String objects and string primitives is done automatically, thus the methods of the String object can be called on string primitives as well.

The valueOf method of the String object can be used to manually convert a String object to a string primitive.

Accessing individual string characters

Individual characters in a string can be accessed by calling the charAt method with the zero-based index of the desired character:

var name = "Jane Doe";
name.charAt(1); // "a"
name.charAt(4); // " "

It's also possible to use the square brackets notation:

name[0]; // "J"

This feature, however, is not supported in all browsers, so it's best to stick with the charAt method.

String Properties

constructor

Returns a reference to the function that created the String object

length

Returns the number of characters in a string

prototype

Allows the addition of properties and methods to all objects

String Methods

charAt(index)

Returns the character at the specified index

charCodeAt(index)

Returns the Unicode value of the character at the specified index

concat(string1 [, string2 [, ...]])

Creates a new string by joining two or more strings

fromCharCode(num1 [, num2 [, ...]])

Returns a string created by converting the specified Unicode values to characters

indexOf(searchString [, offset])

Returns the position of the first occurrence of a string

lastIndexOf(searchString [, offset])

Returns the position of the last occurrence of a string

match(pattern)

Match a regular expression pattern against the input string

replace(pattern, replacement)

Performs a search and replace operation on the input string using a regular expression

search(pattern)

Searches the input string for the given pattern

slice(offset [, length])

Extracts a section of the string and returns a new string containing the extracted characters

split(pattern [, limit])

Splits the input string into an array using a regular expression

substr(offset [, length])

Returns a part of the string beginning at a specified start position, and through the specified number of characters

substring(indexStart , [indexStop])

Returns a part of the string between two specified indices

toLowerCase()

Makes a string lowercase

toString()

Returns a string representation of the String object

toUpperCase()

Makes a string uppercase

valueOf()

Returns the primitive value of the string

See also

• sprintf() for JavaScript
• Regular expressions in JavaScript