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Showing content from https://webplatform.github.io/docs/javascript/Array/indexOf below:

indexOf · WebPlatform Docs

indexOf Summary

Returns the index of the first occurrence of a value in an array.

Syntax

indexOf( searchElement [, fromIndex ])

searchElement: Required. The value to locate in array1.
fromIndex: Optional. The array index at which to begin the search. If fromIndex is omitted, the search starts at index 0.

Return Value

The index of the first occurrence of searchElement in the array, or -1 if searchElement is not found.

Examples

The following examples illustrate the use of the indexOf method.


 var ar = ["ab", "cd", "ef", "ab", "cd"];

 
 document.write(ar.indexOf("cd") + "<br/>");

 

 
 document.write(ar.indexOf("cd", 2) + "<br/>");

 

 
 document.write (ar.indexOf("gh")+ "<br/>");

 

 
 
 document.write (ar.indexOf("ab", -2) + "<br/>");

Remarks

The indexOf method searches an array for a specified value. The method returns the index of the first occurrence, or -1 if the specified value is not found.

The search occurs in ascending index order.

The array elements are compared to the searchElement value by strict equality, similar to the === operator. For more information, see Comparison Operators.

The optional fromIndex argument specifies the array index at which to begin the search. If fromIndex is greater than or equal to the array length, -1 is returned. If fromIndex is negative, the search starts at the array length plus fromIndex.