[Javascript] Prototype 2 Object.create()

最新推荐文章于 2025-08-15 22:56:20 发布

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原文链接：http://www.cnblogs.com/Answer1215/p/3903162.html

文章标签：

#javascript #ViewUI

本文介绍了一种围栏桩对象的构造方法，并通过原型优化来减少内存资源占用。文章详细展示了如何创建围栏桩对象，实现连接及属性设置，并通过原型方式实现了方法共享。

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function Fencepost (x, y, postNum){
  this.x = x;
  this.y = y;
  this.postNum = postNum;
  this.connectionsTo = [];
}
Fencepost.prototype = {
  sendRopeTo: function ( connectedPost ){
    this.connectionsTo.push(connectedPost);
  },
  removeRope: function ( removeTo ){
    var temp = [];
    for(var i = 0; i<this.connectionsTo.length; i++){
      if(this.connectionsTo[i].postNum != removeTo){
        temp.push(this.connectionsTo[i]);
      }
    }
    this.connectionsTo = temp;
  },
  movePost: function (x, y){
    this.x = x;
    this.y = y;
  },
  valueOf: function (){
  return Math.sqrt( this.x*this.x + this.y*this.y );
  },
  toString: function(){
    var list = this.connectionsTo.map(function(each){
        return each.postNum + "\n";
    });
    return 'Fence post #'+this.postNum+":\n"+
      'Connected to posts:'+
      list+"\n"+
      'Distance from ranch: '+this.valueOf()+
      ' yards';
      
  }
};

var genericPost = 
  {x: 0, y: 0, postNum: undefined,
   connectionsTo: undefined,
   sendRopeTo: function ( connectedPost ) {
     if(this.connectionsTo == undefined){
       var postArray = [ ];
       postArray.push(connectedPost);
       this.connectionsTo = postArray;
     } else {
       this.connectionsTo.push(connectedPost);
     }
   }
  };
var post1 = Object.create(genericPost);  //将继承genericPost中所有的属性
var post2 = Object.create(genericPost);
post1.x = -2;
post1.y = 4;
post1.postNum = 1;
post2.x = 5;
post2.y = 1;
post2.postNum = 2;
post1.sendRopeTo(post2);
post2.sendRopeTo(post1);

Below are the data for three posts that need to be created using the genericPost as a prototype (as in the last challenge). The cowboys have given you all the data you’ll need to build each using the prototype and then assign unique property values through modification. Call each of your posts post<number>, just like you did in the last challenge.

x: 0, y: -3,
postNum: 8,
connectionsTo: 10
x: 6, y: 8,
postNum: 9,
connectionsTo: 10
x: -2, y: 3,
postNum: 10,
connectionsTo: 8, 9

The cowboy-devs have prepared a list of additions that need to happen for certain special fence posts. After you’ve built the above three posts, add properties to those post where the cowboy-devs have deemed appropriate.

Any fence posts with an even ‘y’ coordinate have a birdhouse, and therefore have a numBirds property initially set to 0.
Any fence posts connected to Post #9, but are not Post #9, have a property of weathervane initially set to “N”.
Even numbered fence posts have emergency lights, and a lightsOn property initially set to false.

The base fencepost is again provided for your reference. There are many single lines of code to be entered on this one, so be careful to assign all properties necessary.

var genericPost = {
  x: 0, 
  y: 0, 
  postNum: undefined, 
  connectionsTo: undefined,
  sendRopeTo: function ( connectedPost ) {
    if(this.connectionsTo == undefined){
      var postArray = [ ];
      postArray.push(connectedPost);
      this.connectionsTo = postArray;
    } else {
      this.connectionsTo.push(connectedPost);
    }
  }
};
var post8 = Object.create(genericPost);
var post9 = Object.create(genericPost);
var post10 = Object.create(genericPost);
post8.x = 0;
post8.y = -3;
post8.postNum = 8;
post8.sendRopeTo(post10);
post9.x = 6;
post9.y = 8;
post9.postNum = 9;
post9.sendRopeTo(post10);
post10.x = -2;
post10.y = 3;
post10.postNum = 10;
post10.sendRopeTo(post8);
post10.sendRopeTo(post9);
post9.numBirds = 0;
post10.weathervane = "N";
post8.lightsOn = false;
post10.lightsOn = false;

So now that’s there’s eleventy-billion fence posts everywhere, the cowboy-devs have noticed a significant drain on their memory resources. They’d like you to take a look around the Fencepost constructor and see if there’s anything you can add to a prototype, so that every stinkin’ fence post doesn’t have to carry around anything that it could get from just one place.

Below is the current status of the constructor, with some additions the cowboy-devs have made to improve functionality of the fence post objects. Your job is to identify the portions of the constructor that should be available to ALL fenceposts, and put those in a prototype for fence posts. Your answer should include the modified constructor as well as the newly designed prototype for that constructor. Good luck, pardner.

function Fencepost (x, y, postNum){
  this.x = x;
  this.y = y;
  this.postNum = postNum;
  this.connectionsTo = [];
  this.sendRopeTo = function ( connectedPost ){
    this.connectionsTo.push(connectedPost);
  };
  this.removeRope = function ( removeTo ){
  var temp = [];
  for(var i = 0; i<this.connectionsTo.length; i++){
     if(this.connectionsTo[i].postNum != removeTo){
       temp.push(this.connectionsTo[i]);
     }
  }
    this.connectionsTo = temp;
  }
  this.movePost = function (x, y){
    this.x = x;
    this.y = y;
  };
}

Answer:

function Fencepost (x, y, postNum){
  this.x = x;
  this.y = y;
  this.postNum = postNum;
    this.connectionsTo = [];
}

Fencepost.prototype = {
  sendRopeTo: function ( connectedPost ){
    this.connectionsTo.push(connectedPost);
  },
  removeRope: function ( removeTo ){
  var temp = [];
  for(var i = 0; i<this.connectionsTo.length; i++){
     if(this.connectionsTo[i].postNum != removeTo){
       temp.push(this.connectionsTo[i]);
     }
  }
    this.connectionsTo = temp;
  },
  movePost : function (x, y){
    this.x = x;
    this.y = y;
  };  
};