js new操作符

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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>
<script type="text/javascript">
/*没有返回值
function Test1(str) {
this.a = str;
}
//new
var myTest1 = new Test1('myTest1');
alert(myTest1);//object Object
//no new
var myTest1 = Test1('myTest1');
alert(myTest1);//undefined
*/
/*有返回值
function Test2(str) {
this.a = str;
return this.a;
}
//new
var myTest2 = new Test2('myTest2');
alert(myTest2);//object Object myTest2.a就是myTest2
//no new
var myTest2 = Test2('myTest2');
alert(myTest2);//myTest2
*/
/*返回值为new对象
function Test3(str) {
this.a = str;
return new String(this.a);
}
var myTest3 = new Test3('myTest3');
alert(myTest3);//String myTest3
*/
/* new this
function Test4(str) {
this.a = str;
}
//对象的get_string方法
Test4.prototype.get_string = function() {
return this.a;//this指这个新对象 this.a 新对象的a属性值
}
var myTest4 = new Test4('myTest4');
alert(myTest4.get_string());//myTest4
*/
/*js 伪继承伪类
function Test5(str) {
this.a = str;
}
Test5.prototype.get_Test5String = function() {
return this.a;
}
var myTest5 = new Test5('myTest5');
//alert(myTest5.get_Test5String());
function Test6(str) {
this.b = str;
}
Test6.prototype = new Test5('myTest5');//必须放在get_Test6String方法前不然就冲掉了
Test6.prototype.get_Test6String = function() {
return this.b;
}
var myTest6 = new Test6('myTest6');
alert(myTest6.get_Test6String());//myTest6
alert(myTest6.get_Test5String());//myTest5
*/
</script>
</body>
</html>

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