Javascript类构造函数调用方法

Question

在 Java 中，您可以调用方法来帮助您在构造函数中完成一些繁重的工作，但是 javascript 要求首先定义该方法，所以我想知道是否有其他方法可以解决这个问题，或者我是否被迫在定义之后调用执行繁重工作的方法。我更喜欢将实例函数包含在对象/类中，而且我不得不将构造函数放在对象/类的最后面感觉很奇怪。

function Polynomials(polyString)
{
    // instance variables
    this.polys = [];
    this.left = undefined;
    this.right = undefined;

    // This does not work because it's not yet declared
    this.parseInit(polyString);

    // this parses out a string and initializes this.left and this.right
    this.parseInit = function(polyString)
    {
        //Lots of heavy lifting here (many lines of code)
    }

    // A lot more instance functions defined down here (even more lines of code)

    // Is my only option to call it here?
}

Answer 1

这是我会做的:

var Polynomials = function() { 
   // let's use a self invoking anonymous function
   // so that we can define var / function without polluting namespace
   // idea is to build the class then return it, while taking advantage
   // of a local scope.

   // constructor definition
   function Polynomials( value1) (
      this.property1 = value1;
      instanceCount++;
      // here you can use publicMethod1 or parseInit
   }

   // define all the public methods of your class on its prototype.
   Polynomials.prototype = {

     publicMethod1 : function() { /* parseInit()... */ },

     getInstanceCount : function() ( return instanceCount; }

   }

  // you can define functions that won't pollute namespace here
  // those are functions private to the class (that can't be accessed by inheriting classes)
  function parseInit() {
  }

  // you can define also vars private to the class
  //  most obvious example is instance count.
  var instanceCount = 0; 

   // return the class-function just built;
   return Polynomials;

}();

备注:

要求 1:

原型(prototype)函数是可用于类的每个实例的公共(public)方法。

var newInstance = new MyClass();
newInstance.functionDefinedOnPrototype(sameValue);

问题 2: 如果你想要真正的“私有(private)”变量，你必须这样:

function Constructor() {
   var privateProperty=12;
   this.functionUsingPrivateProperty = function() {  
    // here you can use privateProperrty, it's in scope
   }
}

Constructor.prototype = {
    // here define public methods that uses only public properties
    publicMethod1 : function() {
        // here privateProperty cannot be reached, it is out of scope.
    }
}

就个人而言，我只使用属性(不是私有(private)变量)，并使用“”通用约定来通知属性是私有(private)的。所以我可以在原型(prototype)上定义每个公共(public)方法。
之后，任何使用前缀为“”的属性的人都必须承担他/她的责任，这似乎是公平的。 :-)

对于function fn() {}和var fn= function() {}的区别，google或者S.O.对于这个问题，简短的回答是 function fn() {} 获取定义的函数并在整个范围内分配它的值，当 var 获取定义的 var 时，但它的值仅在代码运行评估时评估。