Hacker Read

ulucs · 2021-03-06 08:43:37+00:00

Js doesn't really care about types, and doesn't seem to convert a string "true" into a boolean true:

    > temp0.innerHTML = true // no error
    > "true" == true
    false
    > true == "true"
    false

milliams | karma 2525 | avg karma 5.33 · | 2013-10-15 12:56:52+00:00

Does JavaScript not have something like "bool(value)"?

jQueryIsAwesome | karma 903 | avg karma 1.45 · | 2012-11-15 22:02:55+00:00

Yeah, is one of the things I don't like about JS. The typeof operator should be able to handle those cases. Or a new operator that returns a boolean would be nice.

    if(defined jQuery.unknown.propierties)

Evbn | karma 3114 | avg karma 1.08 · | 2012-08-15 11:10:35

You can't replace a complex concept with a boolean. This isn't JavaScript.

IvanK_net | karma 1919 | avg karma 5.0 · | 2018-09-17 09:57:57+00:00

I don't think it is useful to know the behaviour of JS in such cases. In practice, you rarely compare strings with numbers, or objects with booleans.

I wrote tens of thousands of lines of JS (e.g. this library https://github.com/photopea/UPNG.js ), I never used "===" in my life :D

reply

elwell | karma 4299 | avg karma 1.76 · | 2015-04-08 00:50:37+00:00

That's just negation in JS.

cozuya | karma 138 | avg karma 0.5 · | 2018-09-12 21:13:40+00:00

javascript could be really nice if they fixed these:

0 is falsey

reply

faceplanted | karma 493 | avg karma 2.15 · | 2017-08-18 14:57:53

Javascript lets you do anything wrong if you use == and not === though, I'm pretty sure the machine apocalypse is going to happen because someone types == instead of === at this point.

pcmaffey | karma 2297 | avg karma 3.21 · | 2018-01-14 18:31:58

`0 === false` is maybe the only thing that I actually hate about javascript. Mutability, I understand and thus can deal with it. Scope, no biggie. But resolving a number to false, when all other numbers resolve to true? Inexplicable.

EDIT: `!0`

reply

lyjackal | karma 190 | avg karma 1.67 · | 2019-06-16 00:51:14

Usually it's awful. I wish JavaScript had if else expressions. Sometimes it can help to break up the lines with indents if you need a single expression:

  var myvar = foo < bar
    ? bar
    : bar < baz
      ? baz
      : 0

Udik | karma 2399 | avg karma 1.07 · | 2016-09-12 21:17:55

FWIW, I almost always use ==. Very rarely, if ever, had any problems- probably I'm used to javascript enough to think in advance of the edge cases and use === when I feel it's necessary.

ex_ex_nihilo | karma 79 | avg karma 2.47 · | 2015-10-20 18:12:48+00:00

In the above case, Javascript is coercing the strings to numbers.

=== does no type coercion. You can also coerce types manually. JS is not statically typed, but it is typed.

reply

moralestapia | karma 5625 | avg karma 2.25 · | 2023-08-13 11:17:07

No, JS is not weird, your code is weird.

true + ("true" - 0) ?

"" && -0 ?

Like, can you tell me a language where it does make sense to "apply AND to an empty string and a (negative?) zero"?

If you write code like this, you have much bigger issues than whatever you choose to write your code in.

reply

joshuahedlund | karma 3762 | avg karma 5.02 · | 2013-02-08 16:33:02+00:00

A lot of javascript causes errors if you try to do stuff on non-existent elements:

> document.getElementById("nonexistent").innerHTML = "";

This however will not cause any errors, it just won't do anything:

> $("#nonexistent").html("");

These sort of do-nothing-but-don't-throw-an-error responses can encourage developers to be less careful about making sure elements exist as they are expected, etc.

reply

iamwil | karma 14162 | avg karma 5.22 · | 2010-01-12 13:24:32

I guess in javascript, that's true.

goto11 | karma 5786 | avg karma 2.51 · | 2020-06-06 07:38:50+00:00

It is trivially easy to avoid though, just use === instead of ==.

Most of the JavaScript wtf's are people getting confused by the implicit type conversions (like [] == ![]). If you ask for it, JavaScript will readily convert a string to a number or an object to a boolean. But if you don't like that, just don't rely on implicit conversions.

reply

ttty | karma 777 | avg karma 1.4 · | 2018-09-17 09:02:02+00:00

It's so funny. Anybody still using == with js?

RandomInteger4 | karma 573 | avg karma 0.9 · | 2018-01-14 18:32:29

Unproductive, how?

Also, this isn't a javascript problem; this is a problem of trying to be too clever and not understanding implicit conversion, which happens in many languages.

reply

Kapow | karma 94 | avg karma 2.24 · | 2016-08-12 15:44:27+00:00

JS gets even weirder when you include all the comparison operators.

https://jsfiddle.net/5Yzs6/17/

Did you know undefined is equal to undefined, but not <= undefined or >= undefined?

Or that two instances of the same object/array are not equal (e.g. [-1] != [-1]), but are both <= and >= each other?

Or that /.*/ is non-comparable (only != is true) to all numbers, but greater than [-0.5] and "-0.5", and less than [0] and "0"?

reply

teraflop | karma 15299 | avg karma 6.52 · | 2016-08-12 14:58:31+00:00

That one isn't specific to Javascript, though. If you can find a mainstream language that doesn't have any values that aren't equal to themselves, I'll give you a cookie.

(Going from memory of the last time I tried this challenge, since I can't get it to load at the moment.)

reply