using the "in" operator for two dimensional array with javascript

Question

So I have the following array defined as follows:

        var a = new Array();
            a[1] = new Array();

            a[1][0] = "Computer Science";
            a[1][1] = "Computer Engineering";
            a[1][2] = "Aerospace Engineering";
            a[1][3] = "Engineering (Other)";
            a[1][4] = "Web Development";
            a[1][5] = "Computer Programming";
            a[1][6] = "Android Development";
                    //a[2] through a[n] defined similarly

and at one point, I'm trying to test if a string is contained anywhere in a[i], say "Computer Science", so I do the following:

                 for(j=1; j<n; j++)
                    if("Computer Science" in a[j])
                    {
                              //DO SOMETHING
                    }

However, this ALWAYS returns false, and yet I've verified that a[j] DOES in fact contain the string (in a[j][0]). Any idea why this is happening?

Answer 1

The in operator is used for testing whether a property (name) exists on an object. For example, "5" in a[j] were true - the array has an index 5.

You want to use the indexOf method to check whether an element exists in an array:

if (a[j].indexOf("Computer Science") > -1)
    //DO SOMETHING

Answer 2

this works:

var a = [];
a[0] = [];
a[1] = [];

a[1][0] = "Computer Science";
a[1][1] = "Computer Engineering";
a[1][2] = "Aerospace Engineering";
a[1][3] = "Engineering (Other)";
a[1][4] = "Web Development";
a[1][5] = "Computer Programming";
a[1][6] = "Android Development";

for(j=0; j<a.length; j++) {
    if("Computer Science" in oc(a[j])) {
       alert("test");               
    }
}

function oc(a)
{
  var o = {};
  for(var i=0;i<a.length;i++)
  {
    o[a[i]]='';
  }
  return o;
}

http://jsfiddle.net/SRPEU/