JavascriptStudyMemo

Javascript basic concept.....

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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);

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