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# Prototype indexOf() Method

This method returns the position of the first occurrence of the argument within the array. If the argument doesn't exist in the array, returns -1.

NOTE: First index of the Array starts from zero.

## Syntax:

    array.indexOf(value)  ;

## Return Value :

- Returns the position of the first occurrence of the argument within the array. If the argument doesn't exist in the array, returns -1

## Example:

    <html>
    <head>
    <title>Prototype examples</title>
    <script type="text/javascript"
       src="/javascript/prototype.js">
    </script>
    <script>

    function showResult(){

       var arr = [3, 5, 6, 1, 20];
       alert("Found position : "  + arr.indexOf(6) );
    }

    </script>
    </head>

    <body>

      <p>Click the button to see the result.</p>
      <br />
      <br />
      <input type="button" value="Result" onclick="showResult();"/>

    </body>
    </html>

To understand it in better way you can Try it yourself.

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