Javascript: Adding method to Array type

hydraMax · 10-03-2011, 02:15 PM

I heard it was possible in Javascript to add a method to object types. So I tried adding a method to the Array type, like so:

Code:

Array.prototype.contains = function(elem) {
    for(i in this) {
    	if(elem == this[i]) { return true; }
    }
    return false;
};

...for seeing if an element exists in this array. But whenever I insert this into my code, even without actually using it, it somehow messes up the parsing of the script and causes another function in another part of the script not to be recognized. Do I have the syntax wrong, here?

Guttorm · 10-04-2011, 09:01 AM

Hi

The syntax is ok. I can't think of any reason this will mess up parsing. Are you sure it's inserted in "the right place"?

There could be a problem if some other code also adds a function with the same name. For example, if the array is two dimensional, your function will fail (return false). Maybe some other code expects it to also check multidimensional arrays?

I would try to use a different function name that's not so generic. Does it solve the problem?

hydraMax · 10-04-2011, 12:43 PM

Quote:

Originally Posted by Guttorm

Hi

The syntax is ok. I can't think of any reason this will mess up parsing. Are you sure it's inserted in "the right place"?

There could be a problem if some other code also adds a function with the same name. For example, if the array is two dimensional, your function will fail (return false). Maybe some other code expects it to also check multidimensional arrays?

I would try to use a different function name that's not so generic. Does it solve the problem?

Thanks for the response. To be honest, I had given up on getting an answer and converted my code back to the simpler form, so it is difficult for me to check now. However, I was going to try writing some unit tests later and will try a different name then.

I don't know if this insight helps, but it happens that the other code the failed was actually an array manipulation -- where I pulled an object element from an array and then called a method of that object. The error claimed that the method did not exist. So I am thinking somehow my code damages the Array type.