difference between 'for (var i=0; i < x.length; i++)' and 'for (var iin x)'

[erdibalint]

Hi,

I've come across the problem and I spent a remarkable amount of time
debugging at the end of which I found the cause of the bug to be the
following:

var arr = ['a', 'b', 'c', 'd'];
var arr2 = [];
for (var i=0; i < arr.length; i++) {
var elt = arr[i];
arr2.push(elt);
}
// arr2 equals ["a", "b", "c", "d"]

var arr = ['a', 'b', 'c', 'd'];
var arr2 = [];
for (var i in arr) {
var elt = arr[i];
arr2.push(elt);
}
// arr2 equals ["a", "b", "c", "d", function()]

I thought that the second type of for loop is identical to the first
one and just adds syntetic sugar. I guess I was wrong, can anyone shed
some light on how the two loops are different?

Thank you,
Bálint

[erdibalint]

Re: difference between 'for (var i=0; i &lt; x.length; i++)' and 'for(var i in x)'

Thank you for your clear explanation. Synthetic sugar means a simpler
(more concise or easier to retain) form of an expression that does the
same (has the same semantics) as the more complex one.

On Feb 20, 12:49 pm, RobG <rg...@iinet.ne t.auwrote:

"syntactic sugar"?
>