Question

This is so simple I am baffled. I have the following:

var x = 'shrimp';    
var stypes = new Array('shrimp', 'crabs', 'oysters', 'fin_fish', 'crawfish', 'alligator');
for (t in stypes) {
    if (stypes[t] != x) {
        alert(stypes[t]);
    }
}

Once the values have iterated it starts returning a dozen functions like

function (iterator, context) {
    var index = 0;
    iterator = iterator.bind(context);
    try {
        this._each(function (value) {iterator(value, index++);});
    } catch (e) {
        if (e != $break) {
            throw e;
        }
    }
    return this;
}

What the heck is going on?

Edit: In these scripts I am using http://script.aculo.us/prototype.js and http://script.aculo.us/scriptaculous.js I remember now reading about the way prototype extends arrays and I am betting this is part of it. How do I deal with it?

Answer 1

The for enumeration is going to go over every member of the object you passed it. In this case an array, which happens to have functions as members as well as the elements passed.

You could re-write your for loop to check if typeof stypes[t] == "function" or yada yada. But IMO you are better off just modifying your looping to only elements..

for(var i = 0, t; t = stypes[i]; ++i){
    if (t != x) {
        alert(t);
    }
}

Or

for(var i = 0; i < stypes.length; ++i){
    if (stypes[i] != x) {
        alert(stypes[i]);
    }
}

I wanted to migrate my last comment up to the answer to add the notice of the a caveat for the first type of loop.

from Simon Willison’s “A re-introduction to JavaScript”..

for (var i = 0, item; item = a[i]; i++) {
    // Do something with item
}

Here we are setting up two variables.
The assignment in the middle part of
the for loop is also tested for
truthfulness – if it succeeds, the
loop continues. Since i is incremented
each time, items from the array will
be assigned to item in sequential
order. The loop stops when a “falsy”
item is found (such as undefined).

Note that this trick should only be
used for arrays which you know do not
contain “falsy” values (arrays of
objects or DOM nodes for example). If
you are iterating over numeric data
that might include a 0 or string data
that might include the empty string
you should use the i, j idiom instead.