了解代码在幕后究竟做了什么

Question

我不知道这个问题是否真的被问到，但我有一个带有 for 循环的运行代码，它对数字数组进行排序。但我不明白代码背后的想法。如果有经验的人能告诉我幕后发生的事情，那就太好了。这是代码：

var a = [1, 7, 2, 8, 3, 4, 5, 0, 9];

for(i=1; i<a.length; i++)

  for(k=0; k<i; k++)

    if(a[i]<a[k]){

      var y = a[i]

      a[i]= a[k]

      a[k]=y;

    }

alert(a);

Answer 1

首先，让你的代码正确缩进而不利用可选语法（大括号和分号）将大大有助于你理解代码的处理方式。技术上，大括号不需要与for和if语句，如果只有一个声明，内环路或的分支内执行if。此外，从技术上讲，JavaScript 不要求您在语句的末尾放置分号。不要利用这些可选语法中的任何一种，因为它只会使事情变得更加混乱并可能导致代码中的错误。考虑到这一点，您的代码确实应该如下编写。这段代码的工作是对数组中的项目进行排序。它通过遍历数组并始终检查当前数组项和它之前的项来完成此操作。如果项目无序，则交换值。请参阅注释以了解每行的作用：// Declare and populate an array of numbersvar a = [1, 7, 2, 8, 3, 4, 5, 0, 9];// Loop the same amount of times as there are elements in the array// Although this code will loop the right amount of times, generally// loop counters will start at 0 and go as long as the loop counter// is less than the array.length because array indexes start from 0.for(i=1; i<a.length; i++){&nbsp; // Set up a nested loop that will go as long as the nested counter&nbsp; // is less than the main loop counter. This nested loop counter&nbsp; // will always be one less than the main loop counter&nbsp; for(k=0; k<i; k++){&nbsp; &nbsp; // Check the array item being iterated to see if it is less than&nbsp; &nbsp; // the array element that is just prior to it&nbsp; &nbsp; if(a[i]<a[k]){&nbsp; &nbsp;&nbsp;&nbsp; &nbsp; &nbsp; // ********* The following 3 lines cause the array item being iterated&nbsp; &nbsp; &nbsp; //&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;and the item that precedes it to swap values&nbsp; &nbsp;&nbsp;&nbsp; &nbsp; &nbsp; // Create a temporary variable that stores the array item that&nbsp; &nbsp; &nbsp; // the main loop is currently iterating&nbsp; &nbsp; &nbsp; var y = a[i];&nbsp; &nbsp; &nbsp;&nbsp;&nbsp; &nbsp; &nbsp; // Make the current array item take on the value of the one that precedes it&nbsp; &nbsp; &nbsp; a[i]= a[k];&nbsp; &nbsp; &nbsp;&nbsp;&nbsp; &nbsp; &nbsp; // Make the array item that precedes the one being iterated have the value&nbsp;&nbsp; &nbsp; &nbsp; // of the temporary variable.&nbsp; &nbsp; &nbsp; a[k]=y;&nbsp; &nbsp; }&nbsp; }}&nbsp; &nbsp;&nbsp;alert(a);