How can I check that two objects have the same set of property names?

Question

How can I check that two objects have the same set of property names?

I am using node, mocha, and chai for my application. I want to test that my returned results data property is the same "type of object" as one of my model objects. (Very similiar to chai's instanceof). I just want to confirm that the two objects have the same sets of property names. I am specifically not interested in the actual values of the properties.

Lets say I have the model Person like below. I want to check that my results.data has all the same properties as the expected model does. So in this case, Person which has a firstName and lastName.

So if results.data.lastName and results.data.firstName both exist, then it should return true. If either one doesn't exist, it should return false. A bonus would be if results.data has any additional properties like results.data.surname, then it would return false because surname doesn't exist in Person.

the model

function Person(data) {
  var self = this;
  self.firstName = "unknown";
  self.lastName = "unknown";

  if (typeof data != "undefined") {
     self.firstName = data.firstName;
     self.lastName = data.lastName;
  }
}

javascript
node.js
mocha
chai

Answer 1

You can serialize simple data to check for equality:

data1 = {firstName: 'John', lastName: 'Smith'};
data2 = {firstName: 'Jane', lastName: 'Smith'};
JSON.stringify(data1) === JSON.stringify(data2)

This will give you something like

'{firstName:"John",lastName:"Smith"}' === '{firstName:"Jane",lastName:"Smith"}'

As a function...

function compare(a, b) {
  return JSON.stringify(a) === JSON.stringify(b);
}
compare(data1, data2);

EDIT

If you're using chai like you say, check out http://chaijs.com/api/bdd/#equal-section

EDIT 2

If you just want to check keys...

function compareKeys(a, b) {
  var aKeys = Object.keys(a).sort();
  var bKeys = Object.keys(b).sort();
  return JSON.stringify(aKeys) === JSON.stringify(bKeys);
}

should do it.

Answer 2

If you want to check if both objects have the same properties name, you can do this:

function hasSameProps( obj1, obj2 ) {
  return Object.keys( obj1 ).every( function( prop ) {
    return obj2.hasOwnProperty( prop );
  });
}

var obj1 = { prop1: 'hello', prop2: 'world', prop3: [1,2,3,4,5] },
    obj2 = { prop1: 'hello', prop2: 'world', prop3: [1,2,3,4,5] };

console.log(hasSameProps(obj1, obj2));

In this way you are sure to check only iterable and accessible properties of both the objects.

EDIT - 2013.04.26:

The previous function can be rewritten in the following way:

function hasSameProps( obj1, obj2 ) {
    var obj1Props = Object.keys( obj1 ),
        obj2Props = Object.keys( obj2 );

    if ( obj1Props.length == obj2Props.length ) {
        return obj1Props.every( function( prop ) {
          return obj2Props.indexOf( prop ) >= 0;
        });
    }

    return false;
}

In this way we check that both the objects have the same number of properties (otherwise the objects haven't the same properties, and we must return a logical false) then, if the number matches, we go to check if they have the same properties.

Bonus

A possible enhancement could be to introduce also a type checking to enforce the match on every property.