That's it. That's the meme.
why convert boolean to integer instead of converting the other operand to boolean? it doesn't make sense.
this post was submitted on 05 Aug 2025
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So JavaScript type coercion is odd, but if you understand it and the WHY, it isn’t that bad.
Complain about this instead: https://jsdate.wtf/
God, this is cursed
Javascript's type coercion is rather insane, yes, but there is an actual, practical reason it's done. JS, having been designed to be run in web browsers, wants to avoid blowing up and crashing at all costs. If it gets an unusual type comparison, usually the result of a bug, it tries to return something, such that the script can continue running if at all possible. In JS' mentality, keeping a page running, even if it might not completely function properly, is preferable to throwing an unhandled exception and completely crashing it.
Whether or not that is the right approach is debatable, but there is at least some logic to it. Personally, I think that the proliferation of Node letting JS run outside of browsers exacerbates a lot of JS' issues, but TypeScript does a lot to make it look like a more sensible language.
Hey OP, do you mind checking if your book explains the type coercions that are used with the + operator? I remember it also being mind-boggling, so I was hoping you book could demystify it too.
I don't recall if it covers that sadly. I read it months ago and this part stood out to me.
I mean, it is the basic concept of truthiness. At least they let you use strict equal.
So this is what insanity looks like.
To make it even worse
Mh, '0' is a nonempty string, so !'0' returns false. Then of course !(!'0') would return true. I'd absolutely expect this, Python does the same.
And the second thing is just JavaScript's type coercion shenanigans. In Python
bool('0') # returns True because of nonempty string
bool(int('0')) # returns False because 0 == False
Knowing that JavaScript does a lot of implicit type conversions, stuff like that doesn't strike me as very surprising.
wait hang on...
Is that a tear on the "again"?
Or sweat. Either is appropriate there.
Hello from Perl! Looks reasonable to me!
This is Haverbeke's book, right? Eloquent JavaScript?
It's from Javascript: The Definitive Guide 7th Edition by David Flanagan. It's the O'Reilly book with the rhinoceros on it.
It's the O'Reilly book with the rhinoceros on it.
Honestly O'Reilly should just remove the titles and leave just the animals to describe the books.
This makes it make so much more sense...
Its not really insanity, just a lot of hidden function calls
The description in the first photo about int - steing comparison is incomplete though, right? Wasn't there also a rule anout which one of then comes first (the second parameter gets converted?), and what happens if a string contains non-numeric values?
It's all so confusing…
But then why 2 == true if true is converted to 1
3 - 1 // -> 2
3 + 1 // -> 4
'3' - 1 // -> 2
'3' + 1 // -> '31'
It's not. Just tried in my Browser Console:
2 == true // returns false
I genuinely wasn't aware of that. I must be getting javascript confused for almost any other language. I wonder how many times ive !!'d a value to make that work without actually absorbing that into my head now..
2 is not == true, but !!2 is true
In other languages that shouldn't be equal either though, right?
Maybe you meant
if (2){
console.log("nonzero ints are truthy")
}
else {
console.log("no they're not")
}
Which would output
nonzero ints are truthy
and that would actually work in all languages I know. But that's different from being equal.
Yeah its checking for not null with if isnt it. Maybe thats what has me confused
2 is 'truthy', or rather, not 'falsy'.
I'm not even kidding.
Yes, we should all use rigid types. Name me one language you actually like writing quickly with that has types?
Pyth-oh. Bash-oh. Lisp-oh. Perl-oh. Oh yeah... typed languages suck because of all the boiler
Edit: Fine, Python / Lisp / Perl are all technically "typed" languages, but I ask you what's point of throwing type errors at runtime. Javascript and Rust actually have it right here that the code is either going to run, or it simply isn't. No pussyfooting letting it run first to throw complaints
Python, uh, has types tho? Python just doesn't engage in the same brainless type coercion that JS does, instead type coercion is much more limited and sensible.
Haskell.
Never got into Haskell, but I was taught Miranda at school and thought it was pretty cool
Kotlin is pretty good
Python. Don't know why you excluded it.
I didn't, I'm using the current nomenclature: https://en.wikipedia.org/wiki/Python_(programming_language)#History (last paragraph)
I don't see the image and the last paragraph sais nothing about types.
But Python is a strongly typed language. It's right there in the info box.
Python is un(i)typed.
It's not. It's a strongly typed langage.
"Strongly typed" is meaningless. (Or nearly so; in practice it means "I like this language" and "weakly typed" means "I dislike this language".) The point is that Python has no type system.
You're spewing nonsense.
There absolutely is a type system in Python. The fact that you have dynamic types doesn't preclude having also strong types and certainly doesn't mean you don't have types at all. Try to do 2+"a" in Python and you'll get a TypeError. The thing with Python is that values have a type, not variables. Because all variables are essentially pointers.
Again, "strong types" doesn't mean anything.
But from a type theory perspective, having "dynamic types" absolutely means you don't have a type system. All Python has is runtime exceptions. The fact that one of them is named TypeError doesn't make it a type error in the formal sense.
The point of a type system is not that variables have types, but that types are assigned to expressions (i.e. pieces of code in your source file), not to values (i.e. pieces of data). This is important because it guarantees that certain errors cannot occur in a program that passes the type checker (assuming you have a sensible/useful type system). And you get this assurance without running a single line of code.
To get a similar guarantee from Python, you need to write exhaustive tests, just as with any other runtime error.
That's a very narrow definition of limited usefulness, and in practice it means your code is overly verbose and inflexible. You get stuck with polymorphism everywhere or you're explicitly converting data all the time for nothing.
Plus, if you try to process some data from an external source (which you have to if you want to do anything useful) you don't have any way to test if it's the right type before execution, so you're back at the same place that Python is, without the ability to cleanly recover.
I believe now it is my turn to say you're spewing nonsense. Have you ever used a language with a type system? Because this whole idea of "testing external data to see if it is the right type" doesn't really make sense.
At the lowest layer, generally, external data is an array of bytes. It has no other type you could "test". However, you can decode or parse it into a form that makes sense for your program. And why couldn't I cleanly recover from parse errors? (And how do you think Python does it?)
Clearly you've never programmed anything outside of theoretical computer science or heavily enclosed and controlled systems.