Best way to Check a JavaScript Object has all the keys of another JavaScript Object

Question

I have two JS objects, I want to check if the first Object has all the second Object's keys and do something, otherwise, throw an exception. What's the best way to do it?

function(obj1, obj2){
    if(obj1.HasAllKeys(obj2)) {
         //do something
    }
    else{
         throw new Error(...);
    } 
};

For example in below example since FirstObject has all the SecondObject's key it should run the code :

FirstObject
{
    a : '....',
    b : '...',
    c : '...',
    d : '...'
}
SecondObject
{    
    b : '...',    
    d : '...'
}

But in below example I want to throw an exception since XXX doesnt exist in FirstObject:

FirstObject
{
    a : '....',
    b : '...',
    c : '...',
    d : '...'
}
SecondObject
{    
    b : '...',    
    XXX : '...'
}

Andreas Louv · Accepted Answer · 2015-11-19 21:34:20Z

5

You can use:

var hasAll = Object.keys(obj1).every(function(key) {
  return Object.prototype.hasOwnProperty.call(obj2, key);
});
console.log(hasAll); // true if obj2 has all - but maybe more - keys that obj1 have.

As a "one-liner":

var hasAll = Object.keys(obj1).every(Object.prototype.hasOwnProperty.bind(obj2));

edited Nov 19, 2015 at 21:34

answered Nov 19, 2015 at 21:30

Andreas Louv

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11 Comments

Barmar Over a year ago

Any reason to use .call instead of just obj.hasOwnProperty(key)?

Andreas Louv Over a year ago

@Barmar See: See: stackoverflow.com/questions/12017693/…

Barmar Over a year ago

Hmm, it seems like creating an object that doesn't inherit from Object is a recipe for disaster....

Andreas Louv Over a year ago

Yes my friend, or if you override hasOwnProperty yourself.

Barmar Over a year ago

Although in the latter case, maybe the caller should respect the programmer's replacement. He wanted his object to have custom semantics.

|

tymeJV · Accepted Answer · 2015-11-19 21:30:43Z

5

You can write a function to iterate and check:

function hasAllKeys(requiredObj, secondObj) {
    for (var key in requiredObj) {
        if (!secondObj.hasOwnProperty(key)) {
            return false;
        }
    }

    return true;
}

hasAllKeys(SecondObject, FirstObject);

answered Nov 19, 2015 at 21:30

tymeJV

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3 Comments

Am1rr3zA Over a year ago

I want something to be in one line like python :), can we avoid for loop and checking one by one?

Barmar Over a year ago

Javascript doesn't have list comprehensions, it's harder to make one-liners for things like this.

Andreas Louv Over a year ago

@Am1rr3zA Even if you don't see the iterations they are still happening, if anything the solution that tymeJV have provided is the fastest.

Valerio · Accepted Answer · 2015-11-19 22:18:17Z

1

You can use jQuery's $.map method as follows:
$.map(a,function(value, key) {return b[key];}).length != b.length

edited Nov 19, 2015 at 22:18

answered Nov 19, 2015 at 22:06

Valerio

1104 bronze badges

1 Comment

blm Over a year ago

Using a framework when the original question is clearly looking for plain JavaScript is generally frowned upon (particularly for something as trivial as this), plus, given the typos, you clearly haven't tested it. Answers should either be tested or at least you should mention that you haven't tested it and why.

Doct Jean-Dadet Luyalu · Accepted Answer · 2022-09-06 12:46:41Z

Another way to do this, that seems to work fine as well.

   const o1 = {
              a : '....',
              b : '...',
              c : '...',
              d : '...'
            },

         o2 = {
             b : '...',
             d : '...',
          };

///////////////////////
///// I. IN ONE LINE
///////////////////////
/**/
/**/  if(Object.keys(o2).every(key =>
/**/       key in o1
/**/       // Object.keys(o1).includes(key)
/**/       // Object.keys(o1).filter(x => x==key).length
/**/  ))
/**/  console.log(true);
/**/  else throw new Error("...");
/**/
///////////////////////


///////////////////////
///// II. IN A FUNCTION
///////////////////////
/**/
/**/    var hasAll = (o1 , o2) => {
/**/      let r = Object.keys(o2).every(key =>
/**/        // Object.keys(o1).includes(key)
/**/        // key in o1
/**/        // Object.keys(o1).filter(x => x==key).length
/**/
/**/         Object.keys(o1)
/**/         .reduce((acc,act,arr) =>
/**/            acc && (key in o1) // , true
/**/         )
/**/
/**/      );
/**/      return r;
/**/    }
/**/
/**/ let cond = hasAll(o1 , o2);
/**/
/**/ console.log(cond);
/**/
/**/ if (cond) console.log(true)
//   /**/ else throw new Error("At least, one key doesn'e exist");
/**/
/**/ ////////
/**/
/**/ cond = hasAll(o2 , o1);
/**/
/**/ console.log(cond);
/**/
/**/ if (cond) console.log(true)
/**/ else throw new Error("At least, one key doesn'e exist");
/**/
///////////////////////

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