JavaScript: The Definitive Guide, 6th Edition

Name

String.indexOf() — search a string

Synopsis

string.indexOf(substring)
string.indexOf(substring, start)

Arguments

substring

The substring that is to be searched for within string.

start

An optional integer argument that specifies the position within string at which the search is to start. Legal values are 0 (the position of the first character in the string) to string .length−1 (the position of the last character in the string). If this argument is omitted, the search begins at the first character of the string.

Returns

The position of the first occurrence of substring within string that appears after the start position, if any, or −1 if no such occurrence is found.

Description

String.indexOf() searches the string string from beginning to end to see if it contains an occurrence of substring. The search begins at position start within string, or at the beginning of string if start is not specified. If an occurrence of substring is found, String.indexOf() returns the position of the first character of the first occurrence of substring within string. Character positions within string are numbered starting with zero.

If no occurrence of substring is found within string, String.indexOf() returns −1.

See Also

String.charAt(), String.lastIndexOf(), String.substring()