You are looking for the "indexOf" method. It is available in Mozilla, but not IE. However, it is easy to add support for this to IE (presuming you are ok with the idea of changing the Array.prototype -- there are some reasons why you may not want to do this.)
Here is the official documentation.
Here is a reference implementation, taken from the above page:
if (!Array.prototype.indexOf)
{
Array.prototype.indexOf = function(elt /*, from*/)
{
var len = this.length >>> 0;
var from = Number(arguments[1]) || 0;
from = (from < 0)
? Math.ceil(from)
: Math.floor(from);
if (from < 0)
from += len;
for (; from < len; from++)
{
if (from in this &&
this[from] === elt)
return from;
}
return -1;
};
}
Good luck!