B011-变量输出

function Foo() {
    Foo.a = function() {
        console.log(1)
    }
    this.a = function() {
        console.log(2)
    }
}

Foo.prototype.a = function() {
    console.log(3)
}
Foo.a = function() {
    console.log(4)
}

Foo.a()    // 4
let obj = new Foo();
obj.a()   //2
Foo.a()  // 1