When writing JavaScript, I am usually using the jQuery library. I also seem to work with arrays a lot. Most of the time I only care if an item is an existing array or not. That's pretty simple to do with jQuery, and looks like this:

 1 
 2// First, the array.
 3var mySimpleArray = ["apple", "juice"];
 4 
 5if (!$.inArray("apple", mySimpleArray) == -1) {
 6    // Item is in the array.
 7    console.log("Apple was in the array.");
 8} else {
 9   // Item is not in the array.
10   console.log("Apple was not in the array.");
11}

The takeaway here is that when we use the $.inArray function, we check its value against -1. -1 indicates that the item was not in the array.

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