String.prototype.indexOf()
The indexOf() method returns the index within the calling String object of the first occurrence of the specified value, starting the search at fromIndex. Returns -1 if the value is not found.
Syntax
str.indexOf(searchValue[, *fromIndex*]);
Parameters
searchValue A character/string whose index is to be found.
fromIndex
Optional. The location within the calling string to start the search from. It can be any integer. The default value is 0. If fromIndex < 0
the entire string is searched (same as passing 0). If fromIndex >= str.length
, the method will return -1 unless searchValue
is an empty string in which case str.length
is returned.
Description
Characters in a string are indexed from left to right. The index of the first character is 0, and the index of the last character of a string called str
is str.length - 1
.
Examples
Finding a character in a string
var str1 = "Hello";
console.log(str1.indexOf('H'));
// Console will output: 0
var str1 = "Hello";
console.log(str1.indexOf('Y'));
// Console will output: -1.
indexOf() is case-sensitive
var str1 = "Hello";
console.log(str1.indexOf('ello'));
// Console will output 1
var str1 = "Hello";
console.log(str1.indexOf('Ello'));
// Console will output -1
indexOf() with fromIndex
var str1 = "FreeCodeCamp is a place for people to learn";
console.log(str1.indexOf('Camp'));
// Console will output 8
console.log(str1.indexOf('Camp', 9));
// Console will output -1
Source MDN