在JavaScript中，为什么“反向”循环比“for”快一个数量级？ [英] In JavaScript, why is a "reverse while" loop an order of magnitude faster than "for"?

问题描述

在这些基准测试中，Barbara Cassani表示：一个反向while循环的速度更快，

  while（iterations> 0）{
a = a + 1 ; 
 a = a  -  1; 
迭代 - ; 
} 
  

比通常的for循环：
（i = 0; i a = a + 1;

  
 a = a  -  1; 
 
 
 
 $ b $为什么？
 
 
 更新 
 
 
 
好吧，忘了它，在测试中有一个错误， iterations = 100 ，每页仅执行一次。因此，减少它意味着我们并不真正进入循环。对不起。
解决方案
除了最初的测试中的大错误，以下是结果：
 
 
 
 
   vs  没有区别
 
 
，但> 或< 优于！= =  
 
 
 
 
 
  http://jsperf.com/the-loops/15  
 
In these benchmarks, http://jsperf.com/the-loops, Barbara Cassani showed that a "reverse while" loop is way faster,
while (iterations > 0) {
    a = a + 1;
    a = a - 1;
    iterations--;
}
than a usual "for" loop:
for (i = 0; i < iterations; i++) {
    a = a + 1;
    a = a - 1;
}
Why?

Update

Okay, forget about it, there is a bug in the test, iterations = 100, is executed only once per page. Therefore reducing it, well, means that we don't really enter the loops. Sorry.
解决方案
Except for the big bug in the initial test, here are the results:


for vs while makes no difference
but > or < are better than !==


http://jsperf.com/the-loops/15

                        
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