从现有的javascript Date（）对象获取当前时间？(Get current time from existing javascript Date() object?)

 我正在一个实时的JavaScript应用程序中编写一些调试代码。 在更新循环中，我想： 
 
 
 
 以毫秒为单位获取当前时间 
 
 
 比较最后一帧的时间并打印出帧率 
 
 
 从上面的变量设置最后一帧的当前时间 
 
 
 一切都很简单，除了因为它是在如此性能关键的代码片段中，我试图不打电话 
 
var d=new Date();
 
 我打电话前的每一帧 
 
thisFrameTime = d.getTime();
 
 这可能吗？ 是否有类似的东西： 
 
d.now
 
 哪个更新现有日期对象的时间？ 
 
 我的想法是，我想在调试模式下远离内存分配/ gc，因此它会降低帧速率 - 但也许这不是在javascript中完成的方式？ （我的背景是更多的C / C ++，所以也许这不是思考JS的正确方法？） 
 
 我搜索过谷歌和Stack Overflow，似乎无法找到答案，这让我觉得这是不可能的。 如果是这种情况，确认将有所帮助。 
 
 会不会有任何想法 - 什么是最有效的方法来完成这项工作？ 

I am writing some debug code in a real-time javascript app. In the update loop, I want to:
 
 
 
get current time in milliseconds 
 
 
compare to last frame's time and print out framerate 
 
 
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?

原文：https://stackoverflow.com/questions/8361838