indexof-method-array-javascript.md

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indexOf Method (Array) (JavaScript) | Microsoft Docs		01/18/2017	windows-client-threshold			devlang-javascript		language-reference	JavaScript TypeScript DHTML	arrays [JavaScript], indexOf method indexOf method [JavaScript]	5bee31ae-aaf1-4466-8cfd-ed287e3cdf17	12	mikejo5000	mikejo	ghogen

indexOf Method (Array) (JavaScript)

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

Syntax

  
array1.indexOf(searchElement[, fromIndex])  

Parameters

Parameter	Definition
array1	Required. An array object.
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.

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.

Example

The following examples illustrate the use of the indexOf method.

// Create an array. (The elements start at index 0.)  
var ar = ["ab", "cd", "ef", "ab", "cd"];  
  
// Determine the first location of "cd".  
document.write(ar.indexOf("cd") + "<br/>");  
  
// Output: 1  
  
// Find "cd" starting at index 2.  
document.write(ar.indexOf("cd", 2) + "<br/>");  
  
// Output: 4  
  
// Find "gh" (which is not found).  
document.write (ar.indexOf("gh")+ "<br/>");  
  
// Output: -1  
  
// Find "ab" with a fromIndex argument of -2.  
// The search starts at index 3, which is the array length plus -2.  
document.write (ar.indexOf("ab", -2) + "<br/>");  
// Output: 3  
  

Requirements

[!INCLUDEjsv9]

See Also

JavaScript Methods
Array Object
Using Arrays