let vs var性能

本文介绍了let vs var性能的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述

我一直在阅读有关ES6 Let关键字与现有var关键字的文章.

I've been reading about ES6 Let keyword vs existing var keyword.

我有几个问题.我知道，作用域"是let和var之间的唯一区别，但这对全局意味着什么?

I've got few questions. I understand that "scoping" is the only difference between let and var but what does it mean for the big picture?

function allyIlliterate() { //tuce is *not* visible out here for( let tuce = 0; tuce < 5; tuce++ ) { //tuce is only visible in here (and in the for() parentheses) }; //tuce is *not* visible out here }; function byE40() { //nish *is* visible out here for( var nish = 0; nish < 5; nish++ ) { //nish is visible to the whole function }; //nish *is* visible out here };

现在我的问题:

与var相比，是否拥有任何内存(/性能)优势?

Does let posses any memory(/performance) advantage over var?

除了浏览器支持外，为什么我应该使用let over var的原因是什么?

Other than browser support, what are the reasons why i should be using let over var?

在我的代码工作流程中开始使用let now over var安全吗?

Is it safe to start using let now over var in my code workflow?

谢谢， R

推荐答案

let比node.js中的var慢得多.无论如何，版本为v6.3.0.有时这是戏剧性的.如果用let替换var，下面的代码要慢大约三倍.

let is much slower than var in node.js. Version v6.3.0 anyway. Sometimes this is dramatic. The code below is about three times slower if you replace var with let:

function collatz() { var maxsteps = 0; var maxval = 0; var x = 1; var n; var steps; while (x < 1000000) { steps = 0; n = x; while (n > 1) { if (n & 1) n = 3*n + 1; else n = n / 2; steps += 1; } if (steps > maxsteps) { maxsteps = steps; maxval = x; } x += 1; } console.log(maxval + ' - ' + maxsteps + ' steps'); } collatz();