Javascript Study Memo

Javascript basic concept.....

[@more@]

• Instance property: property defined in constructor:

  function Circle(radius) {
  	this.radius = radius;	
  }
  

• Class property: property belongs to class. all instances share the only copy of class property:

  Circle.PI = 3.141592;
  Circle.UNIT = new Circle(1);
  	
  	

• Instance method:An instance method can be invoked for any instance of a class, but this does not mean that each object contains its own private copy of the method, as it does with instance properties.Instead, instance method is defined by prototype property:

  Circle.prototype.area() { // notes: must explicitly specify thiskeyword to property
  	return Circle.PI * this.radius * this.radius;
  }
  	

• Class method: method associated with a class rather than an instance of a class:

  Circle.max = function (a,b) {
  	if (a.r > b.r) {
  		return a;
  	}else {
  		return b;
  	}
  }
  

---

Function execute & Call Object Concept

When Invoke a function, the function scope is set to scope chain, and then add a new object known as call object to the front of the scope chain. the call object is initialized with parameters, local variable. If a nested function is invoked, the scope chain includes three objects: its own call object, the call object of outer object , and the global object.

uniqueID = function(){ // user can set id back to 0 by: uniqueID.id = 0
    if (!arguments.callee.id) 
        arguments.callee.id = 0;
    return arguments.callee.id++;
};

uid = (function(){ // closure, id is persistent and private
    var id = 0;
    return function(){
        return id++;
    };
})();

var ret = "";
var i = 10;

while (i--) {
    ret += uniqueID() + "t";
    uniqueID.id = 0;
}
alert(ret);

i = 10;
ret = "";
while (i--) {
    ret += uid() + "t";
}
alert(ret);