Here s the test: http://jsperf.com/forloopspeed
如你所看到的那样,这一差异在Safari大,在小得多的程度上,以及在 Chrome和歌剧中。
The analogous thing happens with while loops too: http://jsperf.com/whileloopspeed
My guess is that checking whether i (a Number) is a falsy value is more computationally expensive than checking true/false (the result of the comparison).
I suppose the internal ToBoolean() that is performed on the result of the expression is a bit slower when being given a number as compared to being given a boolean.
In this test I get a difference in performance when converting to boolean from a boolean vs a number using !!.
这与Jaegermonkey特有的问题一样。 如果我接受“追踪仪基”试验,结果就会消失。
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