是否将数组连接到自身比循环遍历数组以创建更多索引更快？

Question

我只是看看three.js github页面上的示例源代码,我遇到了这个ImprovedNoise类,它基本上是一个Perlin噪声脚本:

https://github.com/mrdoob/three.js/blob/master/examples/js/ImprovedNoise.js

在ImprovedNoise函数的最顶层是这样的:

var p = [151,160,137,91,90,15,131,13,201,95,96,53,194,233,7,225,140,36,103,30,69,142,8,99,37,240,21,10,
         23,190,6,148,247,120,234,75,0,26,197,62,94,252,219,203,117,35,11,32,57,177,33,88,237,149,56,87,
         174,20,125,136,171,168,68,175,74,165,71,134,139,48,27,166,77,146,158,231,83,111,229,122,60,211,
         133,230,220,105,92,41,55,46,245,40,244,102,143,54,65,25,63,161,1,216,80,73,209,76,132,187,208,
         89,18,169,200,196,135,130,116,188,159,86,164,100,109,198,173,186,3,64,52,217,226,250,124,123,5,
         202,38,147,118,126,255,82,85,212,207,206,59,227,47,16,58,17,182,189,28,42,223,183,170,213,119,
         248,152,2,44,154,163,70,221,153,101,155,167,43,172,9,129,22,39,253,19,98,108,110,79,113,224,232,
         178,185,112,104,218,246,97,228,251,34,242,193,238,210,144,12,191,179,162,241,81,51,145,235,249,
         14,239,107,49,192,214,31,181,199,106,157,184,84,204,176,115,121,50,45,127,4,150,254,138,236,205,
         93,222,114,67,29,24,72,243,141,128,195,78,66,215,61,156,180];

for (var i=0; i < 256 ; i++) {

    p[256+i] = p[i];

}

您会注意到p填充了一个随机排序的数字0到255的p数组.一旦数组建立,脚本就会for在数组中的每个位置上循环,并有效地从位置256到511锁存自身的副本.顺序相同,但索引移动了256.

所以我的问题是:在JavaScript中循环这样的数组或者简单地执行它是否更快..

p = p.concat(p);

Answer 1

它取决于浏览器:

• Firefox 4使concat的速度提高了约1/2.
• Chrome 11使concat方法的速度提高了10倍.
• IE9给concat方法提供了大约3/4的速度
• Safari 5使concat方法的速度提高了约1/3.
• Opera 11使concat方法的速度提高了约1/4.

亲自尝试一下:

http://jsperf.com/concat-vs-forloop