Javascript和模块模式

Question

i think i did not understand javascript module pattern.

I just create this module:

var mycompany = {};
mycompany.mymodule = (function() {
    var my = {};
    var count = 0;

    my.init = function(value) {
        _setCount(value);
    }

    // private functions
    var _setCount = function(newValue) {
        count = newValue;
    }
    var _getCount = function() {
        return count;
    }

    my.incrementCount = function() {
        _setCount(_getCount() + 1);
    }
    my.degreeseCount = function() {
        _setCount(_getCount() - 1);
    }

    my.status = function() {
        return count;
    }

    return my;
})();


var a = mycompany.mymodule;
var b = mycompany.mymodule;
console.debug(a, 'A at beginning');
console.debug(a, 'B at beginning');
a.init(5);
b.init(2);
console.log('A: ' + a.status()); // return 2 (wtf!)
console.log('B: ' + b.status()); // return 2`

Where is the mistake? I thought that my code would have returned to me not 2 value, but 5.

What's the reason?

Answer 1

a and b are the exact same objects.

var a = mycompany.mymodule;
var b = mycompany.mymodule;

What you want to do is create two different objects which have the same prototype. Something similar to this:

mycompany.mymodule = (function () { 
  var my = function () {};
  my.prototype.init = function (value) {
    _setCount(value);
  };
  my.prototype.incrementCount = ...
  // ...

  return my;
}());

a = new mycompany.mymodule();
b = new mycompany.mymodule();
a.init(5);
b.init(2);

For more info, research "javascript prototypal inheritance"

Answer 2

In JavaScript, objects are passed by reference, not copied.

To explain further, here is a simplified version of your code:

var pkg = (function () {
  var x = {};
  return x;
}());

var a = pkg;
var b = pkg;

You do not create two separate objects but only reference the object pointed at by pkg from both a and b . a and b are exactly the same.

a === b // true

This means that calling a method on a you are ultimately doing the same to b (it points to the same object— x .)

You don't want to use the module pattern for this. You want the usual constructor+prototype.

function Pkg() {
  this.count = 0;
};
Pkg.prototype.init = function (count) { this.count = count; };

var a = new Pkg();
var b = new Pkg();

a === b // false

a.init(2);
a.count === 2 // true
b.count === 2 // false

Answer 3

这是有关模块模式的很好的阅读。