W3School TIY Editor
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<html> <body> <script type="text/javascript"> Array.prototype.indexOf = function (vItem) { for (var i=0; i < this.length; i++) { if (vItem == this[i]) { return i; } } return -1; } var aColors = new Array("red", "green", "blue"); document.write(aColors.indexOf("green")); </script> </body> </html>