Finding this key exist in object or not without loop in js

Question

I have object a and object b .I want to check key of b exist in a or not without using loop how can I do this.

var a = {name1: "hello", game1: "no games", name2: "world"}
var b = {name1:'hello world'}

Yes I can do this using loop. First I can get all the keys of b in array and i can take each key at a time and find by using .hasOwnProperty() but I am looking for the method without using loop how is it possible.

Object.keys(b)[0] in a, but if b has more than one key then you will need a loop, no way around that. — Niet the Dark Absol
– Niet the Dark Absol, Commented Jan 15, 2018 at 14:26
if b is multiple objects then you need to use map Object.keys(b).map(t=>a.hasOwnProperty(t)) — sumeet kumar
– sumeet kumar, Commented Jan 15, 2018 at 14:28
Why the restriction on a loop? All map/reduce/filter are loops too — mplungjan
– mplungjan, Commented Jan 15, 2018 at 14:33
Please update your question to detail if you want to check more than one key from B - people are confused — mplungjan
– mplungjan, Commented Jan 15, 2018 at 14:37
If you don't want loops, use recursion. But what have you gained? — user8897421
– user8897421, Commented Jan 15, 2018 at 14:38

Faly · Accepted Answer · 2018-01-15 14:42:06Z

3

Try this:

var a = {name1: "hello", game1: "no games", name2: "world"};
var b =  {name1:'hello world'};

var exists = Object.keys(a).includes(Object.keys(b)[0])
console.log(exists);

In case there are multiple keys in b to ckeck in a, it should be:

var a = {name1: "hello", game1: "no games", name2: "world"};
var b =  {name1:'hello world', game1: "no games"};

var exists = Object.keys(b).every(bKey => Object.keys(a).includes(bKey));
console.log(exists);

Or just:

var a = {name1: "hello", game1: "no games", name2: "world"};
var b =  {name1:'hello world', game1: "no games"};

var exists = Object.keys(b).every(bKey => bKey in a);
console.log(exists);

edited Jan 15, 2018 at 14:42

answered Jan 15, 2018 at 14:27

Faly

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Comments

kLabz · Accepted Answer · 2018-01-15 14:39:18Z

2

If the keys are not known in advance (and there can be more than one key to check), you can use this trick:

    var a = {name1: "hello", game1: "no games", name2: "world"}
    var b =  {name1:'hello world'}
    
    // Extract keys from a
    var keysA = Object.keys(a);

    // For each key from b, check if a includes it
    // See [1] if needed for every()
    console.log(
      Object.keys(b).every(function(k) { return keysA.includes(k); })
    );

Admittedly, this is very similar to using a loop.

[1] https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/every

edited Jan 15, 2018 at 14:39

answered Jan 15, 2018 at 14:34

kLabz

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Comments

Crunch · Accepted Answer · 2018-01-15 16:17:08Z

1

You can also try underscore.js function _.findKey(object, predicate=_.identity])

Example:-
var users = {
  'barney':  { 'age': 36, 'active': true },
  'fred':    { 'age': 40, 'active': false },
  'pebbles': { 'age': 1,  'active': true }
};

_.findKey(users, function(o) { return o.age < 40; });

Output => 'barney' (iteration order is not guaranteed)

answered Jan 15, 2018 at 16:17

Crunch

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Comments

Aniket Sahrawat · Accepted Answer · 2018-01-15 14:38:46Z

-1

The simplest way is:

console.log('game1' in {name1: "hello", game1: "no games", name2: "world"})

edited Jan 15, 2018 at 14:38

Aniket Sahrawat

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answered Jan 15, 2018 at 14:27

Dmitry Sobolevsky

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4 Comments

user8897421 Over a year ago

@AniketSahrawat: You're making the assumption that the key name is known in advance. If that was the case, then what's the significance of it being an object property?

Cerbrus Over a year ago

This doesn't answer the question. The OP doesn't want to check a single key, but all keys in b.

Dmitry Sobolevsky Over a year ago

Question was: "..I want to check key of b exist in a or not..". Not all keys in b

mplungjan Over a year ago

first I can get all the keys of b in array and i can take each key at a time and find

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