Using a function as an Object's key

Question

I have a function that accepts a function parameter that I'd like to use as the key to an object...

function foo(func) {
    return { func: true };
}

This, of course, returns an object with the string 'func' as the key (not what I want).

Is the right solution to create a string from func and then create the object?

Is there a way to create a hash from a function?

What functionality do you want to achieve? / That you can not when using the functions _name_ as the key...? — fast, Apr 29 '15 at 16:48
The keys in a object are always strings or numbers. Here you can read more :http://stackoverflow.com/questions/6066846/keys-in-javascript-objects-can-only-be-strings — vjdhama, Apr 29 '15 at 16:50

score 1 · Accepted Answer · edited May 23 '17 at 12:06

1

Bearing in mind that object keys are always strings you should be able to use this syntax:

result = {};
result[func] = true;
return result;

edited May 23 '17 at 12:06

Community

1
1

answered Apr 29 '15 at 16:51

D-side

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@sfletche sure. But beware: keys are always strings. And even though other types may appear to work at a first glance, they might bite you with awkward bugs in future. – D-side Apr 29 '15 at 17:04

score 1 · Answer 2 · answered Apr 29 '15 at 17:01

Though you can use functions as keys directly, you can use a hash code function to get the string representation of the function to create integer keys. I got one from http://erlycoder.com/49/javascript-hash-functions-to-convert-string-into-integer-hash-.

function hashFunc(func){
    var str = func.toString();

    var hash = 0;
    if (str.length == 0) return hash;
    for (i = 0; i < str.length; i++) {
        char = str.charCodeAt(i);
        hash = ((hash<<5)-hash)+char;
        hash = hash & hash; // Convert to 32bit integer
    }
    console.log(hash);
    return hash;
}

var col = {}

function add(func) {
    col[hashFunc(func)] = true;
}

function get(func) {
    return col[hashFunc(func)] || false;
}

// test
add(hashFunc);
console.log(get(add)); // false
console.log(get(hashFunc)); // true

Using a function as an Object's key

2 Answers2