Auto-enumeration in Javascript

Question

I want to create C type enumerations, values automatically starting from 0.
What is wrong with the following code?

function ArrayToEnum(arr)
{
    var len = arr.lenght;
    en = {};
    for(i=0;i<len;i++)
        en[arr[i]]=i;
    return en;
}

a=['foo','bar'];
b=ArrayToEnum(arr);
console.debug(b.foo);

> Undefined

I expect it to print 0 but instead(at least in Chromium 9.0) this is undefined. If instead of calling the function, I apply the body directly, it works:

var l=a.length;
for(i=0;i<l;i++) b[a[i]]=i;
console.debug(b.foo);

> 0

What is wrong with the function?

You misspelled length in the 3rd line of your code. Does that error exist in your actual code as well? Also - what's the point of this? — Matt Ball
– Matt Ball, Commented Mar 10, 2011 at 21:22

15ee8f99-57ff-4f92-890c-b56153 · Accepted Answer · 2015-12-18 14:47:13Z

3

If that's your actual code, "length" is misspelled as "lenght" in the third line:

 var len = arr.lenght;

I'd expect that to compile, but it would set len equal to undefined, which would prevent your loop body from executing at all. That would result in arr.foo a.k.a. arr["foo"] being undefined, as you're seeing in your output.

Also you're passing "arr" to ArrayToEnum() when your array in the previous line is called a, not arr.

The common theme here is that when you start talking about a variable you haven't defined yet. JavaScript "helpfully" defines it instead of telling you it doesn't exist yet.

I tried it in the Chrome JS console, and I got "reference error" until I fixed the "a"/"arr" problem. Once that was fixed, I got "undefined" as you describe.

When I fixed "lenght", bingo, it prints "0".

edited Dec 18, 2015 at 14:47

answered Mar 10, 2011 at 21:23

15ee8f99-57ff-4f92-890c-b56153

37.1k7 gold badges68 silver badges123 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Atilla Filiz Over a year ago

"a"/"arr" is copy/paste error, it is correct in the source, but damn i misspelled length. thanks.

Collectives™ on Stack Overflow

Auto-enumeration in Javascript

1 Answer 1

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related