Auto-enumeration in Javascript

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 开发者_运维百科function?

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".