I am writing some debug code in a real-time javascript app. In the update loop, I want to:

1. get current time in milliseconds
2. pare to last frame's time and print out framerate
3. set last frame's time to current time from the variable above

All straightforward, except that since it's in such a performance-critical piece of code, I'm trying not to call

var d=new Date();

every frame before I call

thisFrameTime = d.getTime();

Is this possible? Is there something along the lines of:

d.now

which updates the time in the existing date object?

My thinking is that I want to stay away from memory allocation / gc while in debug mode so it impacts framerate less - but maybe that's just not how it's done in javascript? (My background is more C/C++, so maybe this is not the right way of thinking for JS?)

I have searched Google and Stack Overflow, and can't seem to find an answer, which makes me think it's not possible. If that's the case, confirmation would be helpful.

Would love any thoughts - what's the most performant way to get this done?

I am writing some debug code in a real-time javascript app. In the update loop, I want to:

1. get current time in milliseconds
2. pare to last frame's time and print out framerate
3. set last frame's time to current time from the variable above

All straightforward, except that since it's in such a performance-critical piece of code, I'm trying not to call

var d=new Date();

every frame before I call

thisFrameTime = d.getTime();

Is this possible? Is there something along the lines of:

d.now

which updates the time in the existing date object?

My thinking is that I want to stay away from memory allocation / gc while in debug mode so it impacts framerate less - but maybe that's just not how it's done in javascript? (My background is more C/C++, so maybe this is not the right way of thinking for JS?)

I have searched Google and Stack Overflow, and can't seem to find an answer, which makes me think it's not possible. If that's the case, confirmation would be helpful.

Would love any thoughts - what's the most performant way to get this done?

• javascript
• date
• time

Share Improve this question Follow edited Feb 14, 2013 at 13:40 J. Steen 15.6k1515 gold badges5858 silver badges6464 bronze badges asked Dec 2, 2011 at 19:54 GameMakerGameMaker 9511 silver badge77 bronze badges

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2 Answers 2

Sorted by: Reset to default 4

There is a Date.now() function.

var time = Date.now()

The problem is that it is a part of EcmaScript 5 so older browser (IE 6-8) don't support it. As written on the MDM (link above) you can solve this issue by including this into your code:

if (!Date.now) {  
  Date.now = function() {  
    return +(new Date);  
  };  
}  

You don't control gc in a browser, it runs when it runs. Creating Date objects each time you need the current time is probably the best way to do this and should be trivial unless you're holding references to the objects (which will prevent them from collecting).

However, you should probably use AOP-style profiling code instead of baking "debug code" into your source. I'm not even sure what that is, but it sounds like something you should never do.