Why are Javascript for/in loops so verbose?

Question

I'm trying to understand the reasoning behind why the language designers would make the for (.. in ..) loops so verbose. For example:

for (var x in Drupal.settings.module.stuff) {
    alert("Index: " + x + "\nValue: " + Drupal.settings.module.stuff[x]);
}

It makes trying to loop over anything semi-complex like the above a real pain as you either have to alias the value locally inside the loop yourself, or deal with long access calls. This is especially painful if you have two to three nested loops.

I'm assuming there is a reason why they would do things this way, but I'm struggling with the reasoning.

Answer 1

So your complaint is that the for (var key in set ) loop in Javascript loops the index, and not the values (or both) like foreach ($array as $key => $value) like PHP (and a number of others) do?

I think this is an attempt to be more inline with a standard for-loop, compare:

for (var index = 0; index < set.length; index++) {
    f(set[index]);
}

for (var key in set) {
    f(set[key]);
}

Consistency is achieved this way between the original form, splitting the key/value pair and returning both may well be very useful and indeed I find the JavaScript method a pain, but it is very clean.

What language did it borrow from originally? What is the method there - the Perl/PHP style of foreach() is a different root.

Personally, if I'm using JavaScript, I am using jQuery, and that has jQuery.each():

$.each(set, function(key, value) {
    f(value);  // or f(this); -- though 'this' will be an object in all cases
});