I think "value | 0" is basically same as "Math.floor(value)"

ZitchDog · on Sept 3, 2015

Yes, but it is 18% faster do run the bitwise or on my machine:

https://jsperf.com/or-vs-floor/2

Stormcaller · on Sept 3, 2015

Its because they don't do the same thing

Math.floor() favors the number equal to/less than the parameter, Math.floor(-15.5) is -16 while (-15.5 | 0) is -15

Also because the returned value is int32[0],

Math.floor(2147483648.5) is 2147483648 while (2147483648.5 | 0) is -2147483648

You are fine if you know the input is less than (2^31) + 1 and you want to truncate, rather than floor.

[0]: http://www.ecma-international.org/ecma-262/6.0/#sec-binary-b...

nkron · on Sept 3, 2015

ECMAScript 2016 adds Math.trunc()[0] which should give the same value as | 0 for inputs that fit in 32 bits.

[0] http://www.javascripture.com/Math#trunc

4Data · on Sept 3, 2015

Hmm, pretty sure floor rounds a number downward to its nearest integer. So Math.floor(-15.5) would be 15.

https://developer.mozilla.org/pt-PT/docs/Web/JavaScript/Refe...

Stormcaller · on Sept 3, 2015

Literally the first example on that page:

> Math.floor( 45.95); // 45

> Math.floor(-45.95); // -46

Its not like its hidden or anything... Its in the center of the page on my 1920x1080 screen.

catchmrbharath · on Sept 3, 2015

Nope. Math.floor(-15.5) would be -16. It rounds a number downwards. -16 < -15.

jpollock · on Sept 3, 2015

There is no substantial difference in performance on mine (within 2%), although the OR was always a little bit faster.

Chrome 45 on Linux

It's odd that a bitwise operator should have the effect of truncating the float (since X|0 == X)? I'm guessing there's an implicit type conversion to int in the middle?

TazeTSchnitzel · on Sept 3, 2015

The bitwise operators don't make sense for floating-point values. So they work by converting to a 32-bit integer first.

aaronm67 · on Sept 3, 2015

And every time a developer sees that, they're going to google "bar javascript" "single bar javascript" "bitwise or javascript" "bitwise or javascript effect" until they figure out WTF is going on.

This all to save a fraction of a microsecond on an operation that's called 60 times on the page.

pkstn · on Sept 3, 2015

Actually only 52 :D

But yeah, I agree about googling part: I remember having Googled "tilde javascript" and "pipe javascript".. :)

Tilde is useful with indexOf:

if (~array.indexOf(item)) {}

..equals to:

if (array.indexOf(item) > -1) {}

yellowapple · on Sept 4, 2015

This is the sort of thing that makes Perl readable in comparison to Javascript :)

ldesegur · on Sept 3, 2015

i/13|undefined works too

logicallee · on Sept 3, 2015

plus

  i/13|undefined

has that "this was originally written in javascript, not ported halfheartedly from some other language" feel. (Well, maybe PHP.)

ygra · on Sept 3, 2015

That's just adding another conversion from undefined to Number to Int32 for the right operand. You could probably use false as well. Or the empty string.

irascible · on Sept 4, 2015

gulp I guess I should stop using parseInt :/

robocat · on Sept 7, 2015

value | 0 will always return a 32 bit integer.

Math.floor(value) can return some weirder values such as: NaN (for anything that isn't a number), and Infinity, -Infinity, -0. And Math.floor(-1e-300); is -1 so care needs to be taken with floating values near zero.