How to conditionally create object property in one line?

Question

I want to create a property on an object conditionally. The idea is to ensure the property doesn't exist (so not just null) if it has no value.

What I'm doing right now:

// comes from users
req.query = {
  foo: true
}

// my object which will contains allowed properties IF EXISTS
const where = {}

if (req.query.foo) {
  where.foo = req.query.foo
}
if (req.query.bar) {
  where.bar = req.query.bar
}

console.log(where)

It's really boring to repeat this for every different property...

Is there a way to do it in one line?

EDIT:

I don't want to get all properties from req.query

score 9 · Accepted Answer · edited Jun 03 '21 at 08:43

9

Create object property obj.foo if value exists (or any other condition)

&& operator returns second element if the first boolean condition is fulfilled

es6 spread operator ... does what it does)

const value = 'bar'

const empty = undefined

const obj = {
  ...value && { foo: value }, // read ...(value && { foo: value }) parenthesis are not necessary
  ...empty && { empty },
  ...(100 > 0) && { condition: 'true' },
  ...(100 < 0) && { condition: 'false' },
}

console.log(obj)

edited Jun 03 '21 at 08:43

mbesson

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answered Jun 02 '21 at 14:43

Nikita Mazur

1,602
1
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Sorry... can you explain it ? – mbesson Jun 02 '21 at 14:54
Create object property conditionally `const value` exists so `obj.foo` is created, `const empty` is `undefined` so the property `obj.empty` is not created – Nikita Mazur Jun 02 '21 at 15:02
Thanks, it wasn't clear for me that the spread operator has effect on the right side of the && operator – mbesson Jun 03 '21 at 07:48
@mbesson Yeah, sorry, there is even an eslint rule which adds parenthesis so Its more clear) – Nikita Mazur Jun 03 '21 at 08:44

score 0 · Answer 2 · answered Jun 02 '21 at 14:39

0

You could do:

const merged = {...where, ...req.query};

answered Jun 02 '21 at 14:39

Gpack

1,878
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Thx but req.query contains additional properties and I don't want them in merged – mbesson Jun 02 '21 at 14:42
So then you probably want to use moustafa's answer – Gpack Jun 02 '21 at 14:44

score 0 · Answer 3 · answered Jun 02 '21 at 14:40

0

Try this:

const elements = ["foo", "bar"];

elements.forEach(el => {
    if (req.query[el]) {
        where[el] = req.query[el];
    }
});

answered Jun 02 '21 at 14:40

moustafa

251
2
11

This forces us to create an array of keys and keep it updated, which doesn't look good – Nikita Mazur Jun 02 '21 at 15:23
@NikitaMazur You need to know which keys you're interested in and that is going to be somewhere, why not in a list in one place? – Ben Stephens Jun 02 '21 at 15:43
@BenStephens you're right, you need to keep track of the keys anyways. – moustafa Jun 02 '21 at 19:14

Mohamed Ayadi · Answer 4 · 2021-06-02T14:56:32.053

0

You can simply write it in one line like this :

let where = {};
if (req.query.foo) where = {...where, foo : req.query.foo };
if (req.query.bar) where = {...where, bar : req.query.bar };

I hope that it helps.

edited Jun 02 '21 at 14:56

answered Jun 02 '21 at 14:50

Mohamed Ayadi

83
1
8

Yoni A · Answer 5 · 2021-06-02T15:34:55.323

0

If you want a simple one liner (maybe less readable), you can do:

Object.keys(req.query).forEach(key => req.query[key] && (where[key] = req.query[key]));

edited Jun 02 '21 at 15:34

answered Jun 02 '21 at 15:23

Yoni A

124
8

if req.query.key = undefined, it will create where.key = undefined – Nikita Mazur Jun 02 '21 at 15:25
2

added a check for that – Yoni A Jun 02 '21 at 15:30

score 0 · Answer 6 · answered Jun 02 '21 at 15:56

0

If you're okay adding a pluck function, you could do it like this:

const req = { query: { baz: '1', foo: '3' } };
const where = {};

const pluck = (keys, obj) =>
  keys.reduce((a, k) => typeof obj[k] === 'undefined' ? a : Object.assign(a, { [k]: obj[k] }), {});

const add_foo_bar = (where, query) =>
  Object.assign({}, where, pluck(['foo', 'bar'], query));

const res = add_foo_bar(where, req.query);

console.log(res);

answered Jun 02 '21 at 15:56

Ben Stephens

3,303
1
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8

I think this is the cleaner solution but I was searching for a solution without adding a function – mbesson Jun 08 '21 at 11:44

How to conditionally create object property in one line?

6 Answers6