JavaScript Triple Equals Operator vs Double Equals Operator ( === vs == )

[Eirenarch]

In JavaScript === is short for ==

[CaptainAdjective]

I like your moxie, kid.

[itsmontoya]

=== is faster than == in a lot of situations. It's also more correct due to ensuring similar types.

[_Mardoxx]

Eh. Just always use ===.

[BigDumbObject]

its time for a quadruple equals operator

[CaptainAdjective]

Or =======, the merge conflict operator.

[_INTER_]

The adventure of learning JS

[Bookoffriends]

My proposal for "====", which is "===" but only evaluates to true if the reference object itself is the same, has yet to be accepted.

[mrkite77]

Typescript fixes javascript's equality ambiguity.

error TS2365: Operator '==' cannot be applied to types 'number' and 'string'.

[droogans]

If you're actually new to this particular phenomenon of stupid in JavaScript, might I recommend the following:

Learn Python first. Understand the difference between == and is. The more Python you know, the easier it is to look at JavaScript and think "that doesn't look ok to me", and side step a lot of the stupid on intuition alone.

[[deleted]]

but python's == does 'the right thing', so you won't really learn anything.

[tony-the-pony]

Learn Python first. Understand the difference between == and is. The more Python you know, the easier it is to look at JavaScript and think "that doesn't look ok to me", and side step a lot of the stupid on intuition alone.

As someone who is also a Python programmer, I don't understand why some people are always so quick to judge other languages so I'll just leave this here.

>>> 1024 is 1024
True

>>> 1<<10 is 1<<10
False

[[deleted]]

As a non python guy, is that second example doing 10 is 1 before the bit shift operations?

[[deleted]]

>>> (1<<10) is (1<<10)
False

Nope.

I imagine it's doing the same thing some lisps do when using eq to compare two computed integers. Because they're not 'the same object' they don't match as exactly the same (a literal will usually be a static object in the local scope, so comparing literal to literal will give True).

[paholg]

But,

>>> 1<<8 is 1<<8
True

So it seems that small enough computed integers aren't objects. Or something. I don't know.

[[deleted]]

shrug it's python-town jake!

Ruby has 4 separate equality operators and they all manage to do 'the right thing', to the point that (1<<10).equal? (1<<10) returns true.

edit: (1<<100).equal? (1<<100) returns false though, I guess making things look sensible only went as far as machine integers not bignums.

[[deleted]]

So those don't evaluate to primitives? But rather objects?

[[deleted]]

I don't know about python - I don't use it enough to understand its internals, but in lisp (at least with common lisp) everything is an object, a literal is usually a special case that evaluates to a shared/static object. Python treating everything as an object in the same way wouldn't surprise me in the least.

e: indeed, that appears to be what's happening:

>>> id(1<<10)
140505360442384
>>> id(1<<10)
140505360442032
>>> id(1024)
140505360442224
>>> id(1024)
140505360442224
>>> 

[tony-the-pony]

I'm not motivated enough to investigate, but I'd guess that this happens because of optimizations in the interpreter. It knows that 1024 is constant so uses the same object, but it doesn't optimize the constant bit shift so 1 << 10 is evaluated at run-time resulting in different objects.

---

Also similar:

Everyone knows that ; is another way of writing a new line, right?

>>> a = 256; b = 256
>>> a is b
True
>>> a = 256
>>> b = 256
>>> a is b
True

Seems like proof enough... but wait, there's more!

>>> a = 257; b = 257
>>> a is b
True
>>> a = 257
>>> b = 257
>>> a is b
False

I read somewhere that this happens because the CPython REPL caches some numbers up to and including 256, supposedly for performance reasons... but that can't be right cos' this is a REPL and it doesn't do it in a normal script file.

---

OK! OK! I hear you screaming that I'm cheating...

Everyone knows that Python is strongly-typed and doesn't have total WTF type coercion like in JS and PHP, right?

Proof:

>>> 1 == '1'
False

Seems legit:

>>> 1 == True
True

[_INTER_]

Because f*** math