JavaScript: The Definitive Guide, Fourth Edition

Name

String.substr( ) — extract a substring

Availability

JavaScript 1.2; JScript 3.0; deprecated

Synopsis

                  string.substr(start, length)

Arguments

start

The start position of the substring. If this argument is negative, it specifies a position measured from the end of the string: -1 specifies the last character, -2 specifies the second-to-last character, and so on.

length

The number of characters in the substring. If this argument is omitted, the returned substring includes all characters from the starting position to the end of the string.

Returns

A copy of the portion of string starting at and including the character specified by start and continuing for length characters, or to the end of the string if length is not specified.

Description

substr( ) extracts and returns a substring of string. It does not modify string.

Note that substr( ) specifies the desired substring with a character position and a length. This provides a useful alternative to String.substring( ) and String.splice( ), which specify a substring with two character positions. Note, however, that this method has not been standardized by ECMAScript and is therefore deprecated.

Example

var s = "abcdefg";
s.substr(2,2);   // Returns "cd"
s.substr(3);     // Returns "defg"
s.substr(-3,2);  // Should return "ef"; returns "ab" in IE 4

Bugs

Negative values for start do not work in JScript 3.0 (IE 4). Instead of specifying a character position measured from the end of the string, they specify character position 0.

See Also

String.slice( ...