逆向递归看JavaScript原型

<!DOCTYPE html>
<html lang&#061;"en">
<head>
<meta charset&#061;"UTF-8">
<title>title</title>
<script>
function F1(age) {
this.age &#061; age;
}
function F2(age) {
this.age = age;
}
F2.prototype = new F1(10);
function F3(age) {
this.age = age;
}
F3.prototype = new F2(20);
var f3 = new F3(30);
console.log(f3);
console.log(f3.age);
console.log(f3.__proto__.age);
console.log(f3.__proto__.__proto__.age);
</script>
</head>
<body>
</body>
</html>