Equality comparison between Date and number doesn't work

Question

According to the ECMA script standard, the following code should return true, but it doesn't:

d = new Date() ;
d.setTime(1436497200000) ;
alert( d == 1436497200000 ) ;

Section 11.9.3 says:

8. If Type(x) is either String or Number and Type(y) is Object, return the result of the comparison x == ToPrimitive(y).

Then, section 8.12.8 says that ToPrimitive retuns the result of the valueOf method. Which means that the last line in my example above should be equivalent to:

alert( d.valueOf() == 1436497200000 );

Which does return true, indeed.

Why does the first case not return true?

Answer 1

If you look at the spec at section 8.12.8, you will find this text near the end of the section:

When the [[DefaultValue]] internal method of O is called with no hint, then it behaves as if the hint were Number, unless O is a Date object (see 15.9.6), in which case it behaves as if the hint were String.

^{(Emphasis mine)}

Now, in step 8 / 9 of the The Abstract Equality Comparison Algorithm ^[11.9.3], ToPrimitive(x) and ToPrimitive(y) are called without hint parameter.

The lack of this hint parameter, together with the above text, means that the ToPrimitive method returns the toString() value, on date objects.

As you're probably aware, (new Date()).toString() returns a string representation of the date in American English ^[source]:
"Wed Jul 01 2015 22:08:41 GMT+0200 (W. Europe Daylight Time)"

That a string like that doesn't equal 1436497200000 shouldn't come as a big surprise. ;-)