让我顺间思路清晰的一个无聊调试(关于实例、继承)

function a(){
var a1 = 1,
a2 = 2;
}
var b = new a();
console.log(b.constructor);
console.log(b.prototype);
console.log(b);
b.prototype = {
a1 : '3',
a2 : '4'
}
console.log(b.constructor);
console.log(b.prototype);
console.log(b);

a()
undefined
a {}
a()
Object { a1="3", a2="4"}
a { prototype={...}}