Javascript Study Memo

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 propertyreturn 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;}}

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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);