Why Date.now() | 0 not same as Date.now()

Question

Int Number | 0 will same as source number

But why Date.now() | 0 not same as Date.now()

let t = Date.now()
console.log((t | 0) === t)

Does this answer your question? [Using bitwise OR 0 to floor a number](https://stackoverflow.com/questions/7487977/using-bitwise-or-0-to-floor-a-number) — VLAZ, Mar 06 '20 at 09:16
Did you confuse `Date.now() || 0` with `Date.now() | 0`? The two operators are very different. — Luaan, Mar 06 '20 at 09:28
@Luaan not sure why you'd ever use `Date.now() || 0`. Surely, you will never get a falsy result from executing that method. — VLAZ, Mar 06 '20 at 09:48
@VLAZ Of course not from `Date.now()` itself, I assume the `Date.now()` is just used here to provide a date value, that would be an argument/local in the actual code. — Luaan, Mar 06 '20 at 09:58

score 3 · Accepted Answer · answered Mar 06 '20 at 09:13

Bitwise operators operate on bits as represented by 32 zeros and/or ones. If the number being operated on is outside this range, the result will likely be unintuitive.

For bitwise OR, this limit is reached once the number is 2 ** 31 - 1:

const test = num => console.log((num | 0) === num);
test(2 ** 31 - 1)
test(2 ** 31)
test(2 ** 31 + 1)

Date.now returns the number of milliseconds between the epoch and now, which is a large number (1583486012561 or thereabouts), much larger than the upper limit of 2147483647.

Why Date.now() | 0 not same as Date.now()

1 Answers1