使用underscore.js获取对象作为输出

Question

I am trying to use underscore.js on a simple object:

var tab = {
    1: "obj1",
    4: "obj4",
    8: "obj8"
};

What I want to do is simply remove the elements with a key value higher than n so what I did is:

function trimFrom(obj, n){
    return _(obj).filter(function(el, id){
        return id <= n;
    });
};

var tab2 = trimFrom(tab, 5)

Now, what I am expecting when I display tab2 is:

tab2: Object
 1: "obj1",
 4: "obj4"

But what I am getting is:

tab2: Array[2]
 0: "obj1"
 1: "obj4"

How do you get your output to stay as an object and is there any method to apply directly the result to the object passed as a parameter without having to do something like var tab = trimFrom(tab, 5) and avoid copying the values?

Edit: For those who want to make changes directly on the passed object like me, simply do:

function trimFrom(obj, n){
    for(var key in obj)
        if(key > n)
            delete obj[key];
};

Answer 1

ou could get the object keys, and use .reduce() to reduce the key/values to a new object.

DEMO: http://jsfiddle.net/ubxE5/2/

function trimFrom(obj, n){
    return _.reduce(obj, function(res, val, key){
        if (key <= 5)
            res[key] = val;
        return res
    }, {});
};  //  ^--- the new object

---

So then you can pass the object in if you like as well.

function trimFrom(obj, n, result){
    return _.reduce(obj, function(res, val, key){
        if (key <= 5)
            res[key] = val;
        return res
    }, result);
};  //  ^--- the new object



var new_obj = {};

trimFrom(tab, 5, new_obj)