Fastest way to get specific fields in an Object - Javascript

Question

I have an object:

var obj = { a: 'test1', b: 'test2', c: 'test3', d: 'test4', e: 'test5', f: 'test6', g: 'test7', h: 'test8' }

I want to get result:

res = { a: 'test1', c: 'test3', d: 'test4' }

What is the fastest way to do it?

@Justcode Hmmm, you might want to test that. Particularly test accessing other properties on `obj` after you do it. :-) — T.J. Crowder, Oct 19 '18 at 08:03
@T.J.Crowder shouldn't be a problem with if you are dealing with 1 property. — Just code, Oct 19 '18 at 08:40
@Justcode - Again, you might want to test that. It's well-known that deleting a property blows away object optimization. Even just the one. — T.J. Crowder, Oct 19 '18 at 08:46
@T.J.Crowder you are talking about this? https://stackoverflow.com/a/742653/2630817 — Just code, Oct 19 '18 at 08:48
@Justcode - No, I'm talking about [this](https://stackoverflow.com/a/346022/157247) (see: https://jsperf.com/effect-of-delete-on-performance/1). — T.J. Crowder, Oct 19 '18 at 09:23
@Justcode :-) Of course, it's a bit micro-opt. (And that synthetic benchmark doesn't reveal the problem on Firefox; the delete right after creation gets optimized away I think.) It's just, the OP did specifically say "fastest"... ;-) — T.J. Crowder, Oct 19 '18 at 10:02

score 6 · Accepted Answer · answered Oct 19 '18 at 08:03

6

Directly access the fields:

res = {a: obj.a, c: obj.c, d: obj.d};

answered Oct 19 '18 at 08:03

T.J. Crowder

Atishay Jain · Answer 2 · 2018-10-19T08:05:38.657

1

i think you want to delete key-value pair from the object so for that here's the solution

delete obj[b];

delete obj[e];

or you can use lodash pick

var _ = require('lodash')
_.pick( obj, [a, c, d] )

or create a new Object

var final = {a: obj.a, c: obj.c, d: obj.d}

edited Oct 19 '18 at 08:05

answered Oct 19 '18 at 08:03

Atishay Jain

You might want to test that. Particularly test accessing other properties on `obj` after you do it. :-) `delete` has a significant unfortunate affect on the performance of objects you apply it to. – T.J. Crowder Oct 19 '18 at 08:04
yeah, but i've seen a lot of cases where one need to change the current variable only instead of creating a new one. That's why i've multiple methods. Anyway thanks for pointing that out. :) – Atishay Jain Oct 19 '18 at 08:09
Well, you didn't [when I posted that comment](https://stackoverflow.com/revisions/52888187/1). And `_.pick` is certainly not going to be the "fastest" way (not even remotely). – T.J. Crowder Oct 19 '18 at 08:18

2 Answers2