In JavaScript ES6, how do I take just a few properties from a hash?

Question

I have an object with some properties. I would like to extract a few well-know properties, skipping over any that are not present.

Something like this:

let x = {a: 1, b: 2, c: 3};
let y = take a, b, d from x; // Not real JS!

With y now looking like this:

{a: 1, b: 2} // Note that d is missing!

Is there an operator or method that does this?

You could do `delete in.c`. But not sure if that's what you want, since it also deletes it from in. You could also clone and then delete c. — Luka Jacobowitz, Apr 29 '16 at 09:04
please do not use `in` for a variable name, because its a operator. — Nina Scholz, Apr 29 '16 at 09:05
Deleting `c` does not work because there may be properties `d, e, f...` — sdgfsdh, Apr 29 '16 at 09:06

Luka Jacobowitz · Accepted Answer · 2016-04-29T09:16:53.447

4

Another way to do it is by destructuring:

let {a, b, d} = x;
let y = {a, b, d};

This automatically takes out the properties you want to use. Then you can put them back together with an object literal, which in ES6 doesn't require you to do { a: a, b : b }. You can just write { a, b } instead, if the names are the same.

In this case, a, b and d are also copied.

edited Apr 29 '16 at 09:16

answered Apr 29 '16 at 09:06

Luka Jacobowitz

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1

And it also pollutes your scope with unnecessary variables :P – Felix Kling Apr 29 '16 at 12:13

score 0 · Answer 2 · answered Apr 29 '16 at 09:04

0

Try the following -

out = {a: in.a, b:in.b, d:in.d};
out = JSON.parse(JSON.stringify(out));

answered Apr 29 '16 at 09:04

jaibatrik

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What's the purpose of `out = JSON.parse(JSON.stringify(out));` ? – Felix Kling Apr 29 '16 at 12:13
It's there to remove any property that is undefined. – jaibatrik Apr 29 '16 at 13:42
1

I see... that might be worth pointing out, as well as the drawbacks of this approach. – Felix Kling Apr 29 '16 at 13:43

score 0 · Answer 3 · answered Apr 29 '16 at 09:08

0

var copied = {};
var propertiesToCopy = ['a', 'b'];
for (var key in originalObject) {
  if (originalObject.hasOwnProperty(key) && propertiesToCopy.indexOf(key) != -1) {
    copied[key] = originalObject[key];
  }
}

answered Apr 29 '16 at 09:08

Bruno

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In JavaScript ES6, how do I take just a few properties from a hash?

3 Answers3