Sargis Isoyan Sargis Isoyan - 1 year ago 62
Javascript Question

Comparing a new Object() with another new Object() in JavaScript

I've created two new Objects:

var a = new Object();
var b = new Object();

and after comparing, I have got those results:

var a = new Object();
var b = new Object();
console.log(a == b); //false
console.log(a > b); //false
console.log(b > a); //false
console.log(a >= b); //true
console.log(b >= a); //true

Please explain how this happens?

Answer Source

Object references compared with == or != (or === or !==) are compared based on whether they refer to the same object. If so, they're equal; if not, they're not equal.

But the relational comparison operators (>, <, >=, and <=) don't compare the references, they coerce their operands to something they can compare: Numbers or strings.

In the case of new Object(), that coercion ends up creating a string: "[object Object]". And of course, "[object Object]" >= "[object Object]" is true because they're equal.

So in effect, what you're actually doing is:

console.log(a == b);                 //false
console.log(String(a) > String(b));  //false
console.log(String(b) > String(a));  //false
console.log(String(a) >= String(b)); //true
console.log(String(b) >= String(a)); //true

...but note that other object types coerce differently, because objects can choose how they coerce in this situation (where the spec prefers a number over a string) by implementing/overriding valueOf. For instance, Date objects coerce to a number when you apply a relational operator to them if the other operand can also coerce to number. So you can reliably use dt1 > dt2 to see if dt1 represents a date/time after dt2 — but you can't use dt1 == dt2 to check if dt1 and dt2 (two separate Date objects) have the same date/time in them, because == will check to see if they're the same object instead. Which leads us to this bit of amusement:

var dt1 = new Date(2016, 5, 23);
var dt2 = new Date(2016, 5, 23);
console.log(dt1 < dt2);  // false
console.log(dt1 > dt2);  // false
console.log(dt1 == dt2); // false!

All the gory details can be found in the specification:

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