小编Ami*_*die的帖子

我终于开始用Javascript创建我的第一个小练习程序了.我知道它并不优雅.我已经完成了大部分代码的工作,但是当我运行它几次时,我仍然会得到一个"未定义"的字符串.我不知道为什么.有人会友好地向我解释这个未定义的来源吗？

var work = new Array();
work[1] = "product design";
work[2] = "product system design";
work[3] = "product social media post x5";
work[4] = "product Agent Recruitment system design";
work[5] = "product profile system design";
work[6] = "product Agent testing design";
work[7] = "product customer support";
work[8] = "product promotion";
var course = new Array();
course[1] = "javascript";
course[2] = "mandarin";
course[3] = "javascript practical-Code Academy";
course[4] = "javascript practical-learn Street";
course[5] = "mandarin practical-memrise";
course[6] = "new stuff with …

所以我一直在学习使用C +教授编程概念的计算机科学课程.今天我学到了一个新的概念,我不确定应用于JS,每次计算string.length时都会消耗系统资源.这似乎是一件小事,但它让我想到了巨大的阵列以及它如何加起来.看看这个例子,让我知道循环#2是否确实比第一个更有效并且谢谢:

var weekDay = ["Monday", "Tuesday", "Wednesday"];

//for loop #1
for(i=0; i<weekDay.length; i++){
 //code code code
;}

//for loop #2
for(i=0; var n=weekDay.length; i<n; i++){
 //code code code
;}