JavaScript返回NaN变量返回未定义

Question

我目前正在学习JavaScript，使用相同的代码有2个问题。

1）如果我在var Character function下的代码顶部放置一个，则用大括号括起来。 我可以得到changedXPos(); 命令在控制台中工作，如果不这样做，我会被changedXPos(); 此错误“未捕获的ReferenceError：未在:: 1：1处定义changedXPos”我不确定为什么。

2）在运行代码时，在changedXPos函数中，我得到的值为NaN。 我已经使用了调试器，并且可以看到xPos所有实例都是未定义的。 如果我给xPos = 20 ，那么代码可以正常工作，所以我知道xPos由于某种原因没有表现出应该不知道为什么的方式。

我在代码中添加了注释以显示问题所在。 感谢您的时间

var Character = function(name, xPos, yPos) {
  this.name = name;
  this.xPos = xPos;
  this.yPos = yPos;

  //} this bracket is not commentented out code works, by changedXPos(); in    console but xPos is still undefined

  //create instance of Character
  var ron = new Character("Ronald", 55, 30);
  var jil = new Character("Jill", 25, 45);
  var jas = new Character("Jasmine", 16, 85);

  //create arrary of instance Character
  var characterArray = [ron, jil, jas];

  //create for loop to loop through characterArray
  for (i = 0; i < characterArray.length; i++) {
    console.log(characterArray[i]);
  }

  this.information = function() {

    "My name is: " + this.name + " My X position is: " + this.xPos + " My Y  position is: " + this.yPos;
  }

  this.changedXPos = function(value) {
    // change the x position here
    //debugger;
    var xPos = this.xPos; // if i take this var out i get xPos is undefined 
    //var value = isNaN(parseInt(xPos)) ? 0 : parseInt(xPos);
    for (i = 0; i < characterArray.length; i++) {
      value = xPos + 20;
      console.log(value); // value is NaN or xPos is undefined
    }
  }

  this.changedYPos = function(value) {
    // change the y position here
  }

  Character.prototype.toString = function toString() {
    //var info = // character's name and current position on the screen
    //return info;
  };
} // with this bracket coded out above function is out of code block

Answer 1

看起来这就是您要修复的代码。 为了带您过去，您创建了构造函数Function，然后创建了3个实例，分别名为ron ， jil和jas

然后，在Character的原型链上添加了一堆函数，这些函数重写了toString方法，这会打印出您的自定义方法。

Stack溢出时的可运行脚本似乎可以打印整个对象，但是如果您在代码中运行它，它应该可以工作。

 function Character (name, xPos, yPos) { this.name = name; this.xPos = xPos; this.yPos = yPos; } var ron = new Character("Ronald", 55, 30); var jil = new Character("Jill", 25, 45); var jas = new Character("Jasmine", 16, 85); var characterArray = [ron, jil, jas]; Character.prototype.changedXPos = function(value) { this.xPos = value; } Character.prototype.changedYPos = function(value) { this.yPos = value; } Character.prototype.toString = function() { return "My name is: " + this.name + " My X position is: " + this.xPos + " My Y position is: " + this.yPos; }; //create for loop to loop through characterArray for (i = 0; i < characterArray.length; i++) { console.log(characterArray[i]); } 

Answer 2

查看下面的代码，并检查这是否是您要实现的目标。

 function Character(name, xPos, yPos) { this.name = name; this.xPos = xPos; this.yPos = yPos; this.changedXPos = function(value) { this.xPos = this.xPos + value; } this.changedYPos = function(value) { this.yPos = this.yPos + value; } this.information = function() { return "My name is: " + this.name + " My X position is: " + this.xPos + " My Y position is: " + this.yPos; } } var ron = new Character("Ronald", 55, 30); var jil = new Character("Jill", 25, 45); var jas = new Character("Jasmine", 16, 85); var characterArray =[ron,jil,jas]; function changedXPosition(value) { for(i = 0; i < characterArray.length; i++){ characterArray[i].changedXPos(value); } } function changedYPosition(value){ for(i = 0; i < characterArray.length; i++){ characterArray[i].changedYPos(value); } } changedXPosition(20); changedYPosition(30); for(i = 0; i < characterArray.length; i++){ console.log(characterArray[i].information()); }