for循环效率测试

var testArrs = [],i = 0;
while (i < 40000000) {
testArrs.push(i);
i++;
}

function testForeach (arr) {
console.time("foreach");
var newArr = [];
arr.forEach(function (i) {
newArr.push(i);
});
console.timeEnd("foreach");
}

function testNoDeclare (arr) {
console.time("no declare");
var newArr = [];
for (var i = 0; i < arr.length; i++) {
newArr.push(i);
}
console.timeEnd("no declare");
}

function testUseDeclare (arr) {
console.time("use declare");
var newArr = [];
for (var i = 0, len = arr.length; i < len; i++) {
newArr.push(i);
}
console.timeEnd("use declare");
}

// testForeach(testArrs); // 17.94066006783   18.810510252937  20.686124714573   18.864875889506  18.103756977537
//testUseDeclare(testArrs); // 5.110369837503  6.4151451151633  5.0288213826492  5.0288213826492   4.6754447449496
testNoDeclare(testArrs);  // 6.6054248431555  5.8171231129024  5.0288213826492  5.7355746580486   5.0831870192184