indexOf() JavaScript String Method – How to Get Text Index
Whenever you use indexOf() on a string, the method does the following:
- It searches its calling string for the method's first argument.
- It returns the index position of the first match, or
-1
if the method found no match.
note
A calling string is a string on which you used indexOf()
. So, in "Hello, world!".indexOf("world")
, "Hello, world!"
is the calling string.
Syntax of the indexOf()
Method
Here is indexOf()
's syntax:
callingString.indexOf(valueToFind, startIndex)
The snippet above shows that indexOf()
accepts two arguments: a valueToFind and a startIndex.
Argument 1: valueToFind
A valueToFind
is the first argument accepted by the indexOf()
method. It defines the value you wish to find in the calling string.
Example 1: Find the index of day
"SunDay, Tuesday, and Friday are good Days".indexOf("day");
// The invocation above will return:
12
Example 2: Find the index of Day
"SunDay, Tuesday, and Friday are good Days".indexOf("Day");
// The invocation above will return:
3
Example 3: Find the index of 3
"Day1, day-3, and day 6 are good Days".indexOf(3);
// The invocation above will return:
10
Argument 2: startIndex
The startIndex
argument is optional. It specifies the index position where you want the computer to start searching for the valueToFind
argument.
Example 1: Find the index of day
from the 13th index position
"SunDay, Tuesday, and Friday are good Days".indexOf("day", 13);
// The invocation above will return:
24
The startIndex
argument's default value is 0
. Therefore, if omitted or negative, the search will begin at index 0
.
Here's an example:
"SunDay, Tuesday, and Friday are good Days".indexOf("day", -13);
// The invocation above will return:
12
Example 2: Find the index of Day
from the 4th index position
"SunDay, Tuesday, and Friday are good Days".indexOf("Day", 4);
// The invocation above will return:
37
Suppose startIndex
is greater than the calling string's length. In such a case, the computer will ignore the search.
Here's an example:
"SunDay, Tuesday, and Friday are good Days".indexOf("Day", 75);
// The invocation above will return:
-1
tip
- To find the last occurrence of a string, use
lastIndexOf()
. - Suppose you need to use regular expression as the
valueToFind
argument. In that case, usesearch()
. - To do a global search for all matches, use
match()
.
Overview
indexOf()
searches its calling string for the first occurrence of the method's string argument.
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