CODEWITHSUNDEEP
javascriptunderscore.js
sellmeadog
sellmeadog

Reputation: 7517

Find the common members of two Javascript objects

What is the easiest way to find the common members in two Javascript objects? This question is not about equality. I don't care about the values of each member, just that they exist in both objects.

Here's what I've done so far (using underscore.js):

_.intersection(_.keys({ firstName: 'John' }), _.keys({ firstName: 'Jane', lastName: 'Doe' }))

This gives me a result of ['firstName'] as expected, but I would like to find an easier or more efficient way, preferably vanilla Javascript.

Upvotes: 10

Views: 5922

Answers (4)

real_ate
real_ate

Reputation: 11289

I know this question has already been answered but I wanted to offer an "underscore" way of doing it. I am also hoping that people will discuss the best "underscore" way of doing it here too. 

var user1 = { firstName: 'John' }, user2 = { firstName: 'Jane', lastName: 'Doe' };

_.keys(_.pick(user1, _.keys(user2)))

that is my best shot at it, it doesn't reduct the underscore primitives from the original question so maybe this is the best you can do.

Here is the original question in my format for reference

_.intersection(_.keys(user1), _.keys(user2))

Upvotes: 0

Casey Chu
Casey Chu

Reputation: 25463

This will work for modern browsers:

function commonKeys(a, b) {
    return Object.keys(a).filter(function (key) { 
        return b.hasOwnProperty(key); 
    });
};

// ["firstName"]
commonKeys({ firstName: 'John' }, { firstName: 'Jane', lastName: 'Doe' });

Upvotes: 5

Phrogz
Phrogz

Reputation: 303215

var common = [];
for (var key in obj2) if (key in obj1) common.push(key);

Edit for RobG: If you happen to be working in an environment that includes code that is not your own, and you do not trust the author(s) to have extended Object.prototype correctly, then you might want to do:

var common = [];
for (var k in obj2) if (obj2.hasOwnProperty(k) && obj1.hasOwnProperty(k)) common.push(k);

However, as I have stated in the comments below, I have written an article (with an inflammatory title) about why I believe that this used to be good advice, but is good advice no longer:
http://phrogz.net/death-to-hasownproperty

Upvotes: 2

Peter Olson
Peter Olson

Reputation: 142921

Sure, just iterate through the keys of one object and construct an array of the keys that the other object shares:

function commonKeys(obj1, obj2) {
  var keys = [];
  for(var i in obj1) {
    if(i in obj2) {
      keys.push(i);
    }
  }
  return keys;
}

Upvotes: 12

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