javascript入门笔记（4）——对象

Object

Object
operator
delete

traverse all atrributes

Construction

prototype object
problems

solution



like pairs of key:value

var o = new Object();
var circle = {x:0,y:0, radius:2};

operator

you can dynamically add more attributes and child objects!

var book = new Object();
book.title = "html study";
//you can dynamically add more attributes and child objects!
book.chapter1 = new Object();
book.chapter1.title = "html introduction";

delete

delete book.chapter1;
book.chapter1 = null;

traverse all atrributes

for( var x in o)…

var o = new Object();
o.name = "john";
o.age = "56";
for(var x in o){
alert(o[x]);//john,56
alert(x);//name,age
alert(x.valueOf());//name,age
alert(o.x);//undefined. cuz o doesn't have x attribute
}

Construction

Attention:

this.area = function(){ return this.width*this.height;
}

if you change it like this:

this.area= function(){
return w*h;
}

there could be a problem.

eg:

var r = new Rect(5,10);
r.width = 10;
alert(r.area());//this must update with width

prototype object

shared attribute

function Person(){
Person.prototype.name = "jane";

};
var p1 = new Person();
var p2 = new Person();
p1.name = "john";// assignment
alert(p1.name);//john (from instance)
alert(p2.name);//jane (from prototype)

problems

if the attribute is an array, the push() action will affect all the objects.

solution:

combine prototype and regular construction.