How to check if two vars have the same reference?

How can you check if two or more objects/vars have the same reference?

You use == or === :

var thesame = obj1===obj2;

From the MDN :

> If both operands are objects, then JavaScript compares internal > references which are equal when operands refer to the same object in > memory.

The equality and strict equality operators will both tell you if two variables point to the same object.

foo == bar
foo === bar

For reference type like objects, == or === operators check its reference only.

e.g

let a= { text:'my text', val:'my val'}
let b= { text:'my text', val:'my val'}

here a==b will be false as reference of both variables are different though their content are same.

but if I change it to

a=b

and if i check now a==b then it will be true , since reference of both variable are same now.

As from ES2015, a new method Object.is() has been introduced that can be used to compare and evaluate the sameness of two variables / references:

Below are a few examples:

Object.is('abc', 'abc');     // true
Object.is(window, window);   // true
Object.is({}, {});           // false

const foo = { p: 1 };
const bar = { p: 1 };
const baz = foo;

Object.is(foo, bar);         // false
Object.is(foo, baz);         // true

Demo:

console.log(Object.is('abc', 'abc'));
console.log(Object.is(window, window));
console.log(Object.is({}, {}));

const foo = { p: 1 };
const bar = { p: 1 };
const baz = foo;

console.log(Object.is(foo, bar));
console.log(Object.is(foo, baz));

Note: This algorithm differs from the Strict Equality Comparison Algorithm in its treatment of signed zeroes and NaNs.

Possible algorithm:

Object.prototype.equals = function(x)
{
  var p;
  for(p in this) {
      if(typeof(x[p])=='undefined') {return false;}
  }

  for(p in this) {
      if (this[p]) {
          switch(typeof(this[p])) {
              case 'object':
                  if (!this[p].equals(x[p])) { return false; } break;
              case 'function':
                  if (typeof(x[p])=='undefined' ||
                      (p != 'equals' && this[p].toString() != x[p].toString()))
                      return false;
                  break;
              default:
                  if (this[p] != x[p]) { return false; }
          }
      } else {
          if (x[p])
              return false;
      }
  }

  for(p in x) {
      if(typeof(this[p])=='undefined') {return false;}
  }

  return true;
}