Object-preserving map() function: mapValues

[wilzbach]

This adds the mapValues methods.

It works exactly like map, but preserves the object.

_.map2({a: 1, b: 2}, function(val, key) {
    return val * 2;
});
=> {a: 2, b: 4}

There are at least three issues about this function (#220 #1867 #1887), and as I also do this frequently it would be awesome to get this into underscore.

[megawac]

Remove this, we should always return an object by contract

In contrast to _.map it returns an object

You'll also need to test that case

[wilzbach]

@megawac what is the expected behavior if you use this method with an array?

[megawac]

Try doing Object.keys([1,2,3]), you'll notice no length attribute. It should return an object {0: <x>, 1: <y>, 2: <z>}

[wilzbach]

@megawac corrected - thanks :)

[megawac]

var key = keys[index]

to follow current style + everything travis reports

[wilzbach]

sry for being so ignorant to the coding style warnings.

[megawac]

No worries LGTM after this last minor style change

[jridgewell]

This looks to be a copy of _.map's style, which uses currentKey.

[wilzbach]

It is a nearly 1:1 copy of _map, so I thought keeping the index variable name might make sense ...

[jridgewell]

👍

[megawac]

mind adding a test for _.each([null, void 0, 1, "abc", [], {}], (val) => deepEqual(_.mapValues(val, _.identity), {}))

Also, mind adding a test for inherited values from prototype?

[wilzbach]

Also, mind adding a test for inherited values from prototype?

sth. like this?

var proto = function(){this.a = 1};
proto.prototype.b = 1;
var obj = new proto();
deepEqual(_.mapValues(obj, _.identity), {a: 1});

[megawac]

Yep!, also mind adding {} and [] to that empty list

[megawac]

I'm +1 for this if you mind squashing your commits @greenify.

[wilzbach]

I'm +1 for this if you mind squashing your commits @greenify.

Of couse - sorry for being so noobish ...

[megawac]

Closes #1869

[jashkenas]

This looks good to me. Go for it.