Javascript自己动手实现getter/setter

  虽然ES5中为我们提供了Object.defineProperty方法来设置getter与setter,但此原生方法使用起来并不方便,我们何不自己来实现一个类,只要继承该类并遵循一定的规范就可以拥有媲美原生的getter与setter。

  现在我们定义以下规范:

  取值器跟设值器遵循格式:_xxxGetter/_xxxSetter,xxx代表需要被控制的属性。例如,如果要控制foo属性,则对象需要提供_fooGetter/_fooSetter方法来作为实际的取值器与控制器,这样我们可以带代码中调用obj.get('foo')和obj.set('foo', value)来进行取值与设值;否则调用get与set方法相当于代码:obj.foo和obj.foo = value;

  提供watch函数:obj.watch(attr, function(name, oldValue, newValue){});每次调用set方法时,便会触发fucntion参数。 function中name代表被改变的属性,oldValue是上一次该属性的值,newValue代表该属性的最新值。该方法返回一个handle对象,拥有remove方法,调用remove将function参数从函数链中移除。

  首先使用闭包模式,使用attributes变量作为私有属性存放所有属性的getter与setter:

var Stateful = (function(){      'use strict';        var attributes = {          Name: {              s: '_NameSetter',              g: '_NameGetter',              wcbs: []          }      };            var ST = function(){};            return ST;  })()

  其中wcbs用来存储调用watch(name, callback)时所有的callback。

  第一版实现代码如下:

美洲杯赌球 1美洲杯赌球 2

  1 var Stateful = (function(){    2     'use strict';    3     4     var attributes = {};    5         6     function _getNameAttrs(name){    7         return attributes[name] || {};    8     }    9        10     function _setNameAttrs(name) {   11         if (!attributes[name]) {   12             attributes[name] = {   13                 s: '_'   name   'Setter',   14                 g: '_'   name   'Getter',   15                 wcbs: []    16             }   17         }   18     }   19    20        21     function _setNameValue(name, value){   22         _setNameAttrs(name);   23         var attrs = _getNameAttrs(name);   24         var oldValue = _getNameValue.call(this, name);   25         //如果对象拥有_nameSetter方法则调用该方法,否则直接在对象上赋值。   26         if (this[attrs.s]){   27             this[attrs.s].call(this, value);   28         } else {   29             this[name] = value;   30         }   31            32         if (attrs.wcbs && attrs.wcbs.length > 0){   33             var wcbs = attrs.wcbs;   34             for (var i = 0, len = wcbs.length; i < len; i  ) {   35                 wcbs[i](name, oldValue, value);   36             }   37         }   38     };   39        40     function _getNameValue(name) {   41         _setNameAttrs(name);   42         var attrs = _getNameAttrs(name);   43            44         var oldValue = null;   45         // 如果拥有_nameGetter方法则调用该方法,否则直接从对象中获取。   46         if (this[attrs.g]) {   47             oldValue = this[attrs.g].call(this, name);   48         } else {   49             oldValue = this[name];   50         }   51            52         return oldValue;   53     };   54        55     function ST(){};   56        57     ST.prototype.set = function(name, value){   58         //每次调用set方法时都将name存储到attributes中   59         if (typeof name === 'string'){   60             _setNameValue.call(this, name, value);   61         } else if (typeof name === object) {   62             for (var p in name) {   63                 _setNameValue.call(this, p, name[p]);   64             }   65         }   66            67         return this;   68     };   69        70     ST.prototype.get = function(name) {   71         if (typeof name === 'string') {   72             return _getNameValue.call(this, name);   73         }   74     };   75        76     ST.prototype.watch = function(name, wcb) {   77         var attrs = null;   78         if (typeof name === 'string') {   79             _setNameAttrs(name);   80             attrs = _getNameAttrs(name);   81             attrs.wcbs.push(wcb);   82                83             return {   84                 remove: function(){   85                     for (var i = 0, len = attrs.wcbs.length; i < len; i  ) {   86                         if (attrs.wcbs[i] === wcb) {   87                             break;   88                         }   89                     }   90                        91                     attrs.wcbs.splice(i, 1);   92                 }   93             }   94         } else if (typeof name === 'function'){   95             for (var p in attributes) {   96                 attrs = attributes[p];   97                 attrs.wcbs.splice(0,0, wcb); //将所有的callback添加到wcbs数组中   98             }   99               100             return {  101                 remove: function() {  102                     for (var p in attributes) {  103                         var attrs = attributes[p];  104                         for (var i = 0, len = attrs.wcbs.length; i < len; i  ) {  105                             if (attrs.wcbs[i] === wcb) {  106                                 break;  107                             }  108                         }  109                           110                         attrs.wcbs.splice(i, 1);  111                     }  112                 }  113             }  114         }  115     };  116       117     return ST;  118 })()

View Code

  测试工作:

 1 console.log(Stateful);   2     var stateful = new Stateful();   3        4     function A(name){   5         this.name = name;   6     };   7     A.prototype = stateful;   8     A.prototype._NameSetter = function(n) {   9         this.name = n;  10     };  11     A.prototype._NameGetter = function() {  12         return this.name;  13     }  14       15     function B(name) {  16         this.name = name;  17     };  18     B.prototype = stateful;  19     B.prototype._NameSetter = function(n) {  20         this.name = n;  21     };  22     B.prototype._NameGetter = function() {  23         return this.name;  24     };  25       26     var a = new A();  27     var handle = a.watch('Name', function(name, oldValue, newValue){  28         console.log(name   'be changed from '   oldValue   ' to '   newValue);  29     });  30     a.set('Name', 'AAA');  31     console.log(a.name);  32       33     var b = new B();  34     b.set('Name', 'BBB');  35     console.log(b.get('Name'));  36       37     handle.remove();  38     a.set('Name', 'new AAA');  39     console.log(a.get('Name'), b.get('Name'))

  输出:

function ST(){}  Namebe changed from undefined to AAA  AAA  Namebe changed from undefined to BBB  BBB  new AAA BBB

  可以看到将所有watch函数存放于wcbs数组中,所有子类重名的属性访问的都是同一个wcbs数组。有什么方法可以既保证每个实例拥有自己的watch函数链又不发生污染?可以考虑这种方法:为每个实例添加一个_watchCallbacks属性,该属性是一个函数,将所有的watch函数链都存放到该函数上,主要代码如下:

ST.prototype.watch = function(name, wcb) {          var attrs = null;                    var callbacks = this._watchCallbacks;          if (!callbacks) {              callbacks = this._watchCallbacks = function(n, ov, nv) {                  var execute = function(cbs){                      if (cbs && cbs.length > 0) {                          for (var i = 0, len = cbs.length; i < len; i  ) {                              cbs[i](n, ov, nv);                          }                      }                  }                  //在函数作用域链中可以访问到callbacks变量                  execute(callbacks['_'   n]);                  execute(callbacks['*']);// 通配符              }          }                    var _name = '';          if (typeof name === 'string') {              var _name = '_'   name;          } else if (typeof name === 'function') {//如果name是函数,则所有属性改变时都会调用该函数              _name = '*';              wcb = name;          }          callbacks[_name] = callbacks[_name] ? callbacks[_name] : [];          callbacks[_name].push(wcb);                    return {              remove: function(){                  var idx = callbacks[_name].indexOf(wcb);                  if (idx > -1) {                      callbacks[_name].splice(idx, 1);                  }              }          };      };

美洲杯赌球,  经过改变后整体代码如下:

美洲杯赌球 3美洲杯赌球 4

  1 var Stateful = (function(){    2     'use strict';    3     4     var attributes = {};    5         6     function _getNameAttrs(name){    7         return attributes[name] || {};    8     }    9        10     function _setNameAttrs(name) {   11         if (!attributes[name]) {   12             attributes[name] = {   13                 s: '_'   name   'Setter',   14                 g: '_'   name   'Getter'/*,   15                 wcbs: []*/   16             }   17         }   18     }   19    20        21     function _setNameValue(name, value){   22         if (name === '_watchCallbacks') {   23             return;   24         }   25         _setNameAttrs(name);   26         var attrs = _getNameAttrs(name);   27         var oldValue = _getNameValue.call(this, name);   28            29         if (this[attrs.s]){   30             this[attrs.s].call(this, value);   31         } else {   32             this[name] = value;   33         }   34            35         if (this._watchCallbacks){   36             this._watchCallbacks(name, oldValue, value);   37         }   38     };   39        40     function _getNameValue(name) {   41         _setNameAttrs(name);   42         var attrs = _getNameAttrs(name);   43            44         var oldValue = null;   45         if (this[attrs.g]) {   46             oldValue = this[attrs.g].call(this, name);   47         } else {   48             oldValue = this[name];   49         }   50            51         return oldValue;   52     };   53        54     function ST(obj){   55         for (var p in obj) {   56             _setNameValue.call(this, p, obj[p]);   57         }   58     };   59        60     ST.prototype.set = function(name, value){   61         if (typeof name === 'string'){   62             _setNameValue.call(this, name, value);   63         } else if (typeof name === 'object') {   64             for (var p in name) {   65                 _setNameValue.call(this, p, name[p]);   66             }   67         }   68            69         return this;   70     };   71        72     ST.prototype.get = function(name) {   73         if (typeof name === 'string') {   74             return _getNameValue.call(this, name);   75         }   76     };   77        78     ST.prototype.watch = function(name, wcb) {   79         var attrs = null;   80            81         var callbacks = this._watchCallbacks;   82         if (!callbacks) {   83             callbacks = this._watchCallbacks = function(n, ov, nv) {   84                 var execute = function(cbs){   85                     if (cbs && cbs.length > 0) {   86                         for (var i = 0, len = cbs.length; i < len; i  ) {   87                             cbs[i](n, ov, nv);   88                         }   89                     }   90                 }   91                 //在函数作用域链中可以访问到callbacks变量   92                 execute(callbacks['_'   n]);   93                 execute(callbacks['*']);// 通配符   94             }   95         }   96            97         var _name = '';   98         if (typeof name === 'string') {   99             var _name = '_'   name;  100         } else if (typeof name === 'function') {//如果name是函数,则所有属性改变时都会调用该函数  101             _name = '*';  102             wcb = name;  103         }  104         callbacks[_name] = callbacks[_name] ? callbacks[_name] : [];  105         callbacks[_name].push(wcb);  106           107         return {  108             remove: function(){  109                 var idx = callbacks[_name].indexOf(wcb);  110                 if (idx > -1) {  111                     callbacks[_name].splice(idx, 1);  112                 }  113             }  114         };  115     };  116       117     return ST;  118 })()

View Code

  测试:

console.log(Stateful);      var stateful = new Stateful();            function A(name){          this.name = name;      };      A.prototype = stateful;      A.prototype._NameSetter = function(n) {          this.name = n;      };      A.prototype._NameGetter = function() {          return this.name;      }            function B(name) {          this.name = name;      };      B.prototype = stateful;      B.prototype._NameSetter = function(n) {          this.name = n;      };      B.prototype._NameGetter = function() {          return this.name;      };            var a = new A();      var handle = a.watch('Name', function(name, oldValue, newValue){          console.log(name   'be changed from '   oldValue   ' to '   newValue);      });      a.set('Name', 'AAA');      console.log(a.name);            var b = new B();      b.set('Name', 'BBB');      console.log(b.get('Name'));            a.watch(function(name, ov, nv) {          console.log('* '   name   ' '   ov   ' '   nv);      });            a.set({          foo: 'FOO',          goo: 'GOO'      });            console.log(a.get('goo'));            a.set('Name', 'AAA ');            handle.remove();      a.set('Name', 'new AAA');      console.log(a.get('Name'), b.get('Name'))

  输出:

function ST(obj){          for (var p in obj) {              _setNameValue.call(this, p, obj[p]);          }      }  Namebe changed from undefined to AAA  AAA  BBB  * foo undefined FOO  * goo undefined GOO  GOO  Namebe changed from AAA to AAA   * Name AAA AAA   * Name AAA  new AAA  new AAA BBB

  以上代码就是dojo/Stateful的原理。

 


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