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pakastin

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

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

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

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...

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

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...

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.

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

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?

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

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.

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) {}

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

i/13|undefined works too

plus

  i/13|undefined

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

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.

gulp I guess I should stop using parseInt :/

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.

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