alphabetize an array of objects on some shared key

alphabetize-on.js

function alphabetizeOn(arr, fn) {

    var tmp = [],
        final = [];

    arr.forEach(function (item) {
        var key = fn(item);
        tmp.push(key);
    });

    tmp.sort();

    tmp.forEach(function (item) {
        arr.forEach(function (subitem) {
            if (fn(subitem) === item) {
                final.push(subitem);
            } 
        });
    });

    return final;
}