［JavaScript］擴充方法

2011-11-28

為某個型別擴充方法

   1:  Array.prototype.lookup = function(obj) {

   2:      // TODO

   3:  }

為某個物件擴充方法, 如果重新new 一個物件, JavaScript是依照型別去建立, 故事先訂義之擴充方法, 將全數消失

   1:      var array = [];

   2:      array.lookup = function(){ return true;}

3:

   4:      alert(array.lookup());

5:

   6:      array = [];

   7:      alert(array.lookup()); // Exception


     1:      // 陣列宣告    , 並給予物件擴充方法

     2:      var array = [];

     3:      array.lookup = function(){ return true;}    

     4:      document.write("array.lookup is defined? " + (array.lookup != undefined ) + "<br />");

     5:      // 陣列重新宣告, 原物件擴充方法消失

     6:      array = [];

     7:      document.write("Re-array().lookup is defined? " + (array.lookup != undefined ) + "<br /><br />");

     8:      

     9:      // 名稱空間宣告, 並給予物件擴充方法

    10:      var classA = {};    

    11:      classA.lookup = function() { return true; }

    12:      document.write("classA.lookup is defined? " + (classA.lookup != undefined ) + "<br />");    

    13:      // 名稱空間重新宣告, 原物件擴充方法消失

    14:      classA = {};    

    15:      document.write("Re-classA().lookup is defined? " + (classA.lookup != undefined ) + "<br /><br />");

    16:      

    17:      // 類別宣告-Type 1

    18:      var classB = function(){

    19:          this.lookup = function(){ return true; } // 用this來增加function        

    20:      };    

    21:      document.write("classB() is defined? " + (classB() != undefined) + "<br />" ); // 不可將類別當方法來使用

    22:      var classb = new classB();    

    23:      document.write("new classB().lookup is defined? " + (classb.lookup != undefined ) + "<br /><br />");

    24:      

    25:      // 類別宣告-Type 2

    26:      var classC = function(){

    27:          return { // 用return new 來增加function 

    28:              lookup: function(){ return true;} 

    29:          }

    30:      }

    31:      document.write("classC() is defined? " + (classC() != undefined ) + "<br />" );;    

    32:      var classc = classC();

    33:      document.write("classC().lookup is defined? " + (classc.lookup != undefined ) + "<br />");

    34:      var classc_2 = new classC(); // also do it

    35:      document.write("new classC().lookup is defined? " + (classc_2.lookup != undefined ) + "<br />");

    36:      document.write("classc 1 and 2 are different? " + ( classc != classc_2 ) + "<br /><br />");



 

結果


     1:  array.lookup is defined? true

     2:  Re-array().lookup is defined? false

     3:   

     4:  classA.lookup is defined? true

     5:  Re-classA().lookup is defined? false

     6:   

     7:  classB() is defined? false

     8:  new classB().lookup is defined? true

     9:   

    10:  classC() is defined? true

    11:  classC().lookup is defined? true

    12:  new classC().lookup is defined? true

    13:  classc 1 and 2 are different? true



 

結論: 弱型別的語言, 很容易因為宣告而發生非預期的異常, 要多熟悉宣告的方式, 並一統自己延伸套件的宣告方式, 才能儘量避免異常.

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