CODEWITHSUNDEEP
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Atilla Filiz
Atilla Filiz

Reputation: 2432

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 function?

Upvotes: 0

Views: 357

Answers (1)

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

Reputation: 37059

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".

Upvotes: 3

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