Question

此刻我正在学习javascript，使用相同的代码遇到2个问题。

1）如果将大括号放在var Character function下的代码顶部，请使用大括号。我可以在控制台中使用changedXPos();命令，如果不这样做，我会得到changedXPos();这个错误“未捕获的ReferenceError：未定义的XPos为：1：1”我不是确定原因。

2）在运行代码的changedXPos函数中，我得到的值为NaN。我使用了调试器，可以看到xPos的所有实例都是未定义的。如果我提供xPos = 20的代码可以正常工作，那么我知道xPos出于某种原因并没有表现出来，我不知道为什么。

我已在代码中添加注释以显示问题出在哪里。谢谢您的时间

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

似乎是您想要修复代码的地方。要带您过去，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的原型链上添加了许多函数，这些函数重写了toString方法，这会打印出您的自定义方法。

堆栈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，则应该可以正常工作。

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，然后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());
}

JavaScript返回NaN变量返回未定义

2 个答案: