JavaScript設(shè)計模式之命令模式實例分析

更新時間：2019年01月16日 14:26:58 作者：吳封斌技術(shù)博客

這篇文章主要介紹了JavaScript設(shè)計模式之命令模式,結(jié)合實例形式分析了javascript命令模式的概念、原理、用法及相關(guān)注意事項,需要的朋友可以參考下

本文實例講述了JavaScript設(shè)計模式之命令模式。分享給大家供大家參考，具體如下：

第一，命令模式：

（1）用于消除調(diào)用者和接收者之間直接的耦合的模式，并且可以對(調(diào)用這個過程進行留痕操作)
（2）真的不要亂用這個模式,以為他使你簡單調(diào)用寫法變得非常的復(fù)雜和有些難以理解。
（3）你的業(yè)務(wù)出現(xiàn)了 (回退操作)(重做操作)的需求的時候你就要考慮使用這個模式了。

命令的原理：

一種情況為發(fā)出者直接作用于執(zhí)行者，這樣耦合度很高，另外一種情況為，在發(fā)出者和執(zhí)行者之間增加一個用存儲命令的命令訪問庫也即命令命令模式。

第二，現(xiàn)在我們通過一個需求來學習該模式

需求為：

1.有一個"添加流程的按鈕"單擊的時候就會添加一個新的文本當做流程的描述

2.有"返回","重做" 2個按鈕來完成相應(yīng)的任務(wù)。

第三，界面為

<body>
<input type="text" id="flow">
<input type="button" value="添加新流程" onclick="API.addFlow()">
<br>
<input type="button" value="ctrl+z回退" onclick="API.ret()">
<input type="button" value="ctrl+z+x重做" onclick="API.again()">
<div id= "div01"></div>
<script src="Js/設(shè)計模式第三部分/命令模式/keymaster.min.js"></script>
<script src="Js/設(shè)計模式第三部分/命令模式/uuid.js"></script>
<script src="Js/設(shè)計模式第三部分/命令模式/(18)命令模式.js"></script>
</body>

效果為，

根據(jù)上述圖我們逐步完成

步驟一，定義主應(yīng)用程序----接收者

function manager() {
    this.addFlow=function (id,value) {
        //1.得到目標節(jié)點
      var div=document.getElementById("div01");
      var newFlow=document.createElement("div");
      newFlow.setAttribute("id",id);
      newFlow.innerHTML=value;
      div.appendChild(newFlow);
    }
}

步驟二，為對象（執(zhí)行者）建立命令訪問庫 ---意思是可以通過extcute方法訪問到addFlow方法

manager.prototype.extcute=(function () {
  /*command 命令對象
  * */
  return function (command) {
    return this[command.method](command.id,command.value);
  }
})();

步驟三，初始化主類

var ma = new manager();//可以用該對象，調(diào)用其的東西
//用于存儲"調(diào)用對象命令的"集合
var commands = new Array();
//集合的游標--初始化在末尾
var index = commands.length;

步驟四，客戶端----發(fā)出者

var API=function () {
   this.addFlow=function () {
     //把調(diào)用封裝起來
     var command={
       method:"addFlow",
       id:new UUID().createUUID(),//產(chǎn)生id的插件
       value:document.getElementById("flow").value
     };
     //把調(diào)用對象保存起來,用于回退和重做作用
     commands.push(command);
     //重新定位游標---賦值記錄
     index = commands.length;
     //調(diào)用
     ma.extcute(command);
   };
   /**
    * 用于返回的方法
    */
   this.ret=function () {
     if(index-1<0){
       alert("已經(jīng)到了最后一步了...");
     }else {
       var all=document.getElementById("div01").childNodes;
       document.getElementById("div01").removeChild(all[all.length-1]);
       index=index-1;
     }
   };
   /**
    * 用于重做的方法
    */
   this.again=function () {
     if(index>=commands.length){
       alert("已經(jīng)到了最前面一步了,不能進行重做...");
     }else {
       var command=commands[index];//獲取當前的命令位置
       ma.extcute(command);
       index=index+1;
     }
   }
}

步驟五，實例化客戶端

API=new API();//實例化

這樣html中的事件就可以起作用了。

在這里我們使用插件來讓其功能支持自定義的鍵盤事件，插件名稱為：keymaster.js

首先，如html中一樣引入文件，

然后值調(diào)用key添加自定義的鍵盤事件

//添加支持ctrl+z--返回
key("ctrl+z",function () {
  API.ret();
});
//重做---
key("ctrl+shift+x",function () {
  API.again();
})

為此我們可以使用鍵盤的指定組合實現(xiàn)和鼠標點擊一樣的效果。

這里需要說明一下客戶端的API中的id值，也是通過插件來動態(tài)生成的------插件名稱為：uuid.js。這里附上源碼

/*
uuid.js - Version 0.2
JavaScript Class to create a UUID like identifier
Copyright (C) 2006-2008, Erik Giberti (AF-Design), All rights reserved.
This program is free software; you can redistribute it and/or modify it under
the terms of the GNU General Public License as published by the Free Software
Foundation; either version 2 of the License, or (at your option) any later
version.
This program is distributed in the hope that it will be useful, but WITHOUT ANY
WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A
PARTICULAR PURPOSE. See the GNU General Public License for more details.
You should have received a copy of the GNU General Public License along with
this program; if not, write to the Free Software Foundation, Inc., 59 Temple
Place, Suite 330, Boston, MA 02111-1307 USA
The latest version of this file can be downloaded from
http://www.af-design.com/resources/javascript_uuid.php
HISTORY:
6/5/06   - Initial Release
5/22/08 - Updated code to run faster, removed randrange(min,max) in favor of
     a simpler rand(max) function. Reduced overhead by using getTime()
     method of date class (suggestion by James Hall).
KNOWN ISSUES:
- Still no way to get MAC address in JavaScript
- Research into other versions of UUID show promising possibilities
 (more research needed)
- Documentation needs improvement
*/
// On creation of a UUID object, set it's initial value
function UUID(){
  this.id = this.createUUID();
}
// When asked what this Object is, lie and return it's value
UUID.prototype.valueOf = function(){ return this.id; }
UUID.prototype.toString = function(){ return this.id; }
//
// INSTANCE SPECIFIC METHODS
//
UUID.prototype.createUUID = function(){
  //
  // Loose interpretation of the specification DCE 1.1: Remote Procedure Call
  // described at http://www.opengroup.org/onlinepubs/009629399/apdxa.htm#tagtcjh_37
  // since JavaScript doesn't allow access to internal systems, the last 48 bits
  // of the node section is made up using a series of random numbers (6 octets long).
  //
  var dg = new Date(1582, 10, 15, 0, 0, 0, 0);
  var dc = new Date();
  var t = dc.getTime() - dg.getTime();
  var h = '-';
  var tl = UUID.getIntegerBits(t,0,31);
  var tm = UUID.getIntegerBits(t,32,47);
  var thv = UUID.getIntegerBits(t,48,59) + '1'; // version 1, security version is 2
  var csar = UUID.getIntegerBits(UUID.rand(4095),0,7);
  var csl = UUID.getIntegerBits(UUID.rand(4095),0,7);
  // since detection of anything about the machine/browser is far to buggy,
  // include some more random numbers here
  // if NIC or an IP can be obtained reliably, that should be put in
  // here instead.
  var n = UUID.getIntegerBits(UUID.rand(8191),0,7) +
      UUID.getIntegerBits(UUID.rand(8191),8,15) +
      UUID.getIntegerBits(UUID.rand(8191),0,7) +
      UUID.getIntegerBits(UUID.rand(8191),8,15) +
      UUID.getIntegerBits(UUID.rand(8191),0,15); // this last number is two octets long
  return tl + h + tm + h + thv + h + csar + csl + h + n;
}
//
// GENERAL METHODS (Not instance specific)
//
// Pull out only certain bits from a very large integer, used to get the time
// code information for the first part of a UUID. Will return zero's if there
// aren't enough bits to shift where it needs to.
UUID.getIntegerBits = function(val,start,end){
  var base16 = UUID.returnBase(val,16);
  var quadArray = new Array();
  var quadString = '';
  var i = 0;
  for(i=0;i<base16.length;i++){
    quadArray.push(base16.substring(i,i+1));
  }
  for(i=Math.floor(start/4);i<=Math.floor(end/4);i++){
    if(!quadArray[i] || quadArray[i] == '') quadString += '0';
    else quadString += quadArray[i];
  }
  return quadString;
}
// Numeric Base Conversion algorithm from irt.org
// In base 16: 0=0, 5=5, 10=A, 15=F
UUID.returnBase = function(number, base){
  //
  // Copyright 1996-2006 irt.org, All Rights Reserved.
  //
  // Downloaded from: http://www.irt.org/script/146.htm
  // modified to work in this class by Erik Giberti
  var convert = ['0','1','2','3','4','5','6','7','8','9','A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P','Q','R','S','T','U','V','W','X','Y','Z'];
  if (number < base) var output = convert[number];
  else {
    var MSD = '' + Math.floor(number / base);
    var LSD = number - MSD*base;
    if (MSD >= base) var output = this.returnBase(MSD,base) + convert[LSD];
    else var output = convert[MSD] + convert[LSD];
  }
  return output;
}
// pick a random number within a range of numbers
// int b rand(int a); where 0 <= b <= a
UUID.rand = function(max){
  return Math.floor(Math.random() * max);
}
// end of UUID class file

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希望本文所述對大家JavaScript程序設(shè)計有所幫助。

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