===

JPDev@programming.dev to Programmer Humor@programming.dev – 666 points –
76

I still don't understand the === operator

Edit: I think a more type strict ==? Pretty sure I understand the point of typescript now.

So in JavaScript there’s the assignment

=

and the comparator is

==

Since there’s no types JS will do implicit conversion before comparison when using == in a case like this

if(false == '0'){
    //this is true
}

But with === it doesn’t. It means literally compare these

if(false === '0'){
    //this is false
}else{
    //so this will execute instead 
}

But this, however, will

var someState = false;
 if(someState === false){
    //this is true
}
2 more...
> 1 == 1
true
> 1 == '1'
true
> 1 === '1'
false

(from node REPL)

Basically it's the real equals sign perfection

The short answer is that your language needs === when it fucked up the semantics of ==, but it's also too popular and you can't fix it without breaking half the web.

Or when it is something like Prolog, where equality is inherently a messy and complex concept.

JS's == has some gotchas and you almost never want to use it. So === is what == should have been.

All examples are true:

"1" == true
[1, 2] == "1,2" 
" " == false
null == undefined

It isn't that insane. But some invariants that you may expect don't hold.

"" == 0
"0" == 0
"" != "0"

One neat feature is you can compare to both null and undefined at the same time, without other falsey values giving false positives. Although that's not necessary as often now that we have nullish coalescing and optional chaining.

I just tested and Terser will convert v === null || v === undefined to null==v. Personally I would prefer to read the code that explicitly shows that it is checking for both and let my minifier/optimizer worry about generating compact code.

Try changing to const === variable. That’s most likely what’s it doing to minimize the risk of accidental assignment.

Wut? This is an automated optimizer. It is not worried about accidental assignment.

I agree it shouldn’t. But I’ve seen linters that automatically change it since they seem to be forcing practical conventions sometimes.

It's also important if you're checking hashes (at least, it was - if you're using correct hashing algorithm that isn't ancient, you will not have this problem).

Because if you take for example "0e462097431906509019562988736854" (which is md5("240610708"), but also applicable to most other hashing algorithms that hash to a hex string), if("0e462097431906509019562988736854" == 0) is true. So any other data that hashes to any variantion of "0e[1-9]+" will pass the check, for example:

md5("240610708") == md5("hashcatqlffzszeRcrt")

that equals to

"0e462097431906509019562988736854" == "0e242700999142460696437005736231"

which thanks to scientific notation and no strict type checking can also mean

0^462097431906509019562988736854^ == 0^242700999142460696437005736231^

which is

0 == 0 `

I did use md5 as an example because the strings are pretty short, but it's applicable to a whole lot of other hashes. And the problem is that if you use one of the strings that hash to a magic hash in a vulnerable site, it will pass the password check for any user who's password also hashes to a magic hash. There's not really a high chance of that happening, but there's still a lot of hashes that do hash to it.

If you're checking passwords, you should be using constant time string checking, anyway.

More likely, you should let your bcrypt library do it for you.

The other comments explains it in pretty good detail, but when I was learning my teacher explained it sort of like a mnemonic.

1 + 1 = 2 is read "one plus one equals two"

1 + 1 == 2 is read "one plus one is equal to two"

1 + 1 === 2 is read "one plus one is really equal to two"

And you hit the nail on the head, is that === is type explicit while == is implicit.

I'd use something like:

= becomes

== equals

=== is identical to

It's funny how everyone thinks "equals" in this context should be "identical to" when, in normal language, it doesn't really mean that at all!

3 more...

JS devs should have a font that turns == into ≈.

I wish the assignment operator wasn’t the equal sign.

x 👈 5

In Haskell, it's the same as the mathematical = symbol.

Mathematica also has an === operator. And :=.

It's also very language specific, like Pascal/Delphi also have ":=" for assignments and "=" for comparison, etc

What does the walrus operator do?

I think it's called 'delayed assignment'. So it is almost like =, but you can use arguments to define functions, f[a_]:=a+2.

==== when

==    same (after magic)
===   same and same type (in Javascript)
====  same and same type and same actual type (in the backend before conversion to JSON)
===== same and same type and same actual type and same desired type (what the customer wanted)

1 + false ? (I have no idea in which order JS would evaluate things as I rarely have to touch that language much anymore)

I'm JavaScript developer. I love coding WebApps. JS sucks💩.