Question

I need to generate a couple of objects from lists in Javascript. In Python, I’d write this:

{key_maker(x): val_maker(x) for x in a_list}

Another way to ask is does there exist something like jQuery.map() which aggregates objects? Here’s my guess (doesn’t work):

var result = {}
$.map(a_list, function(x) {
    $.extend(result, {key_maker(x): val_maker(x)})
})

Answer 1

Assuming a_list is an Array, the closest would probably be to use .reduce().

var result = a_list.reduce(function(obj, x) {
    obj[key_maker(x)] = val_maker(x);
    return obj;
}, {});

Array comprehensions are likely coming in a future version of JavaScript.

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You can patch non ES5 compliant implementations with the compatibility patch from MDN.

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If a_list is not an Array, but a plain object, you can use Object.keys() to perform the same operation.

var result = Object.keys(a_list).reduce(function(obj, x) {
    obj[key_maker(a_list[x])] = val_maker(a_list[x]);
    return obj;
}, {});