如何在用Javascript构建对象的过程中调用函数？

Question

I want to create an object and run two of its methods on object creation. So if my object is

function newObj(){
this.v1 = 10;
this.v2 = 20;
this.func1 = function(){ ....};
this.func2 = function(){...};
}

and the call to the object is

var temp = new newObj();

I want to run func1() and func2() without calling them explicity on temp variable, like temp.func1() . I want them to be called when I create the new Object variable. I tried putting this.func1() inside the newObj declaration but it doesn't seem to work.

Answer 1

Add method invocation statements in constructor:

function newObj(){
this.v1 = 10;
this.v2 = 20;
this.func1 = function(){ ....};
this.func2 = function(){...};

}

I think it is solution of your needs.

Answer 2

Just call it from within the constructor itself it works just fine: http://jsfiddle.net/yahavbr/tTf9d/

The code is:

function newObj(){
    this.v1 = 10;
    this.v2 = 20;
    this.func1 = function() { alert("func1"); };
    this.func2 = function() { alert("func2"); };

    this.func1();
    this.func2();
}

Answer 3

This works for me in Chrome:

function newObj(){
  this.v1 = 10;
  this.v2 = 20;
  this.func1 = function(){ this.v1 += 1; };
  this.func2 = function(){ alert(this.v1); };
  this.func1();
  this.func2();
}
var obj = new newObj();

Answer 4

Try wrapping it in an self invoking function if you never plan on reusing it, like this:

function newObj(){
    this.v1 = 10;
    this.v2 = 20;
    this.func1val = (function(){ alert('called from c\'tor'); })();
    this.func2val = (function(){ return 2 + 1; })();
}

var temp = new newObj();
alert('temp.func2val = ' + temp.func2val);

DEMO

Answer 5

Using Self invoking function we can call and we can also share parent parameter by doing some work around public variable var that = this;

function newObj(){

this.v1 = 10; // public variable
this.v2 = 20; // public variable
var that = this;  // Allow access to parent function variable to inner function
   (function(){
     // access parent function variable
     // using 'that' ex: 
       that.v1 = 50;
     //fun1code stuff 
   })();

   (function(){
     // access parent function variable
     // using 'that' ex: 
     that.v2 = 60;
     //fun2code stuff 
   })();
}

var temp = new newObj();
console.log(temp.v1);  // output 50
console.log(temp.v2);  // output 60

Answer 6

I think perhaps it needs to be stresed that in JavaScript you need to define the object's functions (or methods, if you prefer that term) before you call them .

For example, if you want to call this.func1() upon instantiation:

var new_object = new newObj();  // create/instantiate an object

function newObj(){
  this.v1 = 10;
  this.v2 = 20;

  this.func1();  //  <-- calling it here causes an error

  this.func1 = function(){ ....};
  this.func2 = function(){ ....};
  this.func3 = function(){ ....};
}

TypeError: this.func1 is not a function

This is a problem I came across years ago when trying to understand how to do OOP in JS. Because in other languages like Java or PHP, you have a constructor function/method usually at the top of your class, and beneath you write in your other functions/methods.

So it would seem logical to write your class thus: 1) define your object's properties, and then 2) list the things you want to do when the object is instantiated, and then 3) list the other class functions/methods.

BUT NO!!

With JavaScript, you must define the object's functions before you call them .

So if you want to call two methods on object creation/instantiation, lets say this.func1() and this.func2() , first define everything in your class and at the end place your method calls:

var new_object = new newObj();  // create/instantiate an object

function newObj(){
  this.v1 = 10;
  this.v2 = 20;

  this.func1 = function(){ ....};
  this.func2 = function(){ ....};
  this.func3 = function(){ ....};

  this.func1();  //  <-- it works here!
  this.func2();  //  <-- it works here!
}

If you wanted to have your code organised with a constructor method placed at the top of other class methods (like previously mentioned, how PHP and Java do it) then you could make a little this._constructor() method and place things there, and call it at the end of your class:

function newObj(){
  this.v1 = 10;
  this.v2 = 20;

  this._constructor = function(){  // do constructor things here
    this.func1();
    this.func2();
  }
  this.func1 = function(){ ....};
  this.func2 = function(){ ....};
  this.func3 = function(){ ....};

  this._constructor();  // call just one method here, nice and tidy
}

Some may say it's kinda redundant, but whatever helps to make your workflow faster... :)

Just for the record, if you want to pass some argument when creating/instantiating an object, say you wanted to have the option to set this.v1 then you could do it like this:

function newObj(set_v1){
  this.v1 = 10;
  this.v2 = 20;

  this._constructor = function(set_v1){  // do constructor things here
    if ( set_v1 != undefined ){  // you can come up with a better condition here
      this.v1 = set_v1;
    }
    this.func1();
    this.func2();
  }
  this.func1 = function(){ ....};
  this.func2 = function(){ ....};
  this.func3 = function(){ ....};

  this._constructor(set_v1);  // call the constructor here and pass the argument
}