Javascript Date getTime() code snippet with mysterious additional characters

Question

<script language="JavaScript">
var t = new Date();
t.getTime() + -864e5;
</script>

What is that funky code after the "+" at the end of the second line doing?

It is probably made to be hard to understand, since I suspect it's one of the ways they try to protect themselves against scraping.

That's a number literal: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Values,_variables,_and_literals#Floating-point_literals. — Felix Kling, Aug 21 '13 at 13:57
possible duplicate of [What number does 8e3 evaluate to?](http://stackoverflow.com/questions/9180772/what-number-does-8e3-evaluate-to) — Bergi, Aug 21 '13 at 14:06

score 25 · Accepted Answer · edited Feb 24 '17 at 10:37

25

It is a valid JavaScript number that represents the number of milliseconds in a 24 hour day.

1000*60*60*24 or 86400000 or 864e5

edited Feb 24 '17 at 10:37

Simon Steinberger

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answered Aug 21 '13 at 13:57

cocco

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4

No idea why anyone would want to use this method - it really makes the code much harder to read... So hard even that you might need to post a question on [so] to understand it :P – Lix Aug 21 '13 at 13:58
@Mattis: It negates the number. Like `5` and `-5`. https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Arithmetic_Operators#-_.28Unary_Negation.29 . Of course it would be easier to just write `a - b` instead of `a + (-b)` but well... – Felix Kling Aug 21 '13 at 13:58
@Mattis: No, it's just to make the script shorter. It doesn't really complicate scraping, every floating point number parser supports this format. – Bergi Aug 21 '13 at 14:04

score 4 · Answer 2 · answered Aug 21 '13 at 14:01

4

-864e5 means "minus 1 day". So the JavaScript is really getting the date/time 24 hours ago.

answered Aug 21 '13 at 14:01

mynetx

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25

score 2 · Answer 3 · answered Jan 11 '17 at 02:44

2

864e5 is a valid JavaScript number that represents the number of milliseconds (a millisecond is 1/1000'th of a second) in a 24 hour day.

1000*60*60*24 = 86400000 or using exponential notation 864e5

answered Jan 11 '17 at 02:44

e3495026

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score 1 · Answer 4 · answered Aug 21 '13 at 14:00

1

It looks like the + -864e5 is offsetting the time 1 day into the past.

Its true its not very readable, or makes much sense to people looking at it for a first time, but there isn't really any other way in bare js (at this point).

answered Aug 21 '13 at 14:00

Shade

775
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`getTime()` returns milliseconds. – mynetx Aug 21 '13 at 14:02
bummer. I was hoping the math above in cocco's anwser was resulting in days. post edited. – Shade Aug 21 '13 at 14:04
Sure there's other ways. You could write out the number in regular notation if you're worried about people not understanding if you use scientific. Or if you're worried about people not knowing the significance of `86400000`, you could put a comment explaining that. And why use `+ -864e5` and not just `- 864e5`? – flarn2006 Aug 01 '17 at 15:45

Javascript Date getTime() code snippet with mysterious additional characters

4 Answers4