Javascript面向对象的5种写法

定义Circle类，拥有成员变量r，常量PI和计算面积的成员函数area()
Javascript代码

//第1种写法 

function Circle(r) { 

this.r = r; 

} 

Circle.PI = 3.14159; 

Circle.prototype.area = function() { 

return Circle.PI * this.r * this.r; 

} 

var c = new Circle(1.0); 

alert(c.area()); 

Javascript代码

//第2种写法 

var Circle = function() { 

var obj = new Object(); 

obj.PI = 3.14159; 

obj.area = function( r ) { 

return this.PI * r * r; 

} 

return obj; 

} 

var c = new Circle(); 

alert( c.area( 1.0 ) ); 

Javascript代码

//第3种写法 

var Circle = new Object(); 

Circle.PI = 3.14159; 

Circle.Area = function( r ) { 

return this.PI * r * r; 

} 

alert( Circle.Area( 1.0 ) ); 

Javascript代码

//第4种写法 

var Circle={ 

"PI":3.14159, 

"area":function(r){ 

return this.PI * r * r; 

} 

}; 

alert( Circle.area(1.0) ); 

Javascript代码

//第5种写法 

var Circle = new Function("this.PI = 3.14159;this.area = function( r ) {return r*r*this.PI;}"); 

alert( (new Circle()).area(1.0) );