I am trying to use .indexOf to find out if an array contains a string. Something is causing an error, but I don't know what. I'm sure this is a really simple thing, but I don't know the language and so don't see it. What's wrong?

//this code creates an error in IE
var myMines=new Array();
var newMine="22";
var myVar = myMines.indexOf(newMine);   //when I comment out this line, the page does not generate an error

• javascript

Are you, by chance, using IE 8 (or lower)? Array.indexOf only works in IE 9+, Firefox 3+, and Chrome 7+.

Source: http://kangax.github.com/es5-compat-table/

Docs for Array.indexOf (also includes a function to implement this in browsers that don't support it): https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/Array/indexOf

Before being added in some modern browsers indexOf was exclusively a function used to search a string for another string and return the starting index. You are trying to use this function on an empty array and I'm guessing in a browser that does not support the indexOf function for arrays.

All you are doing it creating an array, and then seeing if something exists in it.

newMine is simply a value that you are attempting to look for inside an empty array. Try populating the array first.

What you do is basically:

• creating an Array;
• creating a variable;
• forget to add it to the array;
• asking an array for the position of an item that is nou in the array.

I've just posted your code into my Firebug console (running Firefox 11) and it worked. As your array is "empty" here, indexOf() just returns -1. Maybe you're script just can't handle a -1 value. However, I believe this code should work in most browsers. Who knows, maybe you've just found a bug in chrome's javascript implementation (^^).

The IndexOf returns the current index/position (0 base) of a string, i.e.

var myMines="Hello World";
var myVar = myMines.indexOf('W');
alert(myVar); // Will alert 6 because 'W' is at the 7th position (first index is 0) so index is 6