JavaScript: The Definitive Guide, 5th Edition

Name

String.substring( ): return a substring of a string — ECMAScript v1

Synopsis

string.substring(from, to)

Arguments

from

A nonnegative integer that specifies the position within string of the first character of the desired substring.

to

A nonnegative optional integer that is one greater than the position of the last character of the desired substring. If this argument is omitted, the returned substring runs to the end of the string.

Returns

A new string, of length to-from, which contains a substring of string. The new string contains characters copied from positions from to to−1 of string.

Description

String.substring( ) returns a substring of string consisting of the characters between positions from and to. The character at position from is included, but the character at position to is not included.

If from equals to, this method returns an empty (length 0) string. If from is greater than to, this method first swaps the two arguments and then returns the substring between them.

It is important to remember that the character at position from is included in the substring but that the character at position to is not included in the substring. While this may seem arbitrary or counterintuitive, a notable feature of this system is that the length of the returned substring is always equal to to-from.

Note that String.slice( ) and the nonstandard String.substr( ) can also extract substrings from a string. Unlike those methods, String.substring( ) does not accept negative arguments.

See Also