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.

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.

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
}

> 1 == 1
true
> 1 == '1'
true
> 1 === '1'
false

(from node REPL)

Basically it’s the real equals sign