js创建对象的几种方法

//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()

Java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());

//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());

Java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 ) );

//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 ) );

Java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 ) );

//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 ) );

Java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) );

//第4种写法
var Circle={
"PI":3.14159,
"area":function(r){
return this.PI * r * r;
}
};
alert( Circle.area(1.0) );

Java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) );