javascript advance

inheritance.js

function Mammal() {};
Mammal.prototype.sayHello = function() {
    alert("Hello from mammal");
}
// inheritance step 1
function Cat() {
    Mammal.call(this);
}
// inheritance step 2 (extends)
Cat.prototype = Object.create(Mammal.prototype);

// inheritance step 3 (constructor)
Cat.prototype.constructor = Cat;
Cat.prototype.sayHello = function() {
    // polymorphism
    Mammal.prototype.sayHello.call(this);
    alert("Hello from cat");
}
var cat = new Cat();
cat.sayHello();

promise.js

var promise = function() {
    return new Promise(function(resolve, reject) {
        setTimeout(function() {
            document.getElementById("promise").innerHTML = "yay!";
            resolve();
        }, 2000);
    });
}

promise().then(function() {
   document.getElementById("wrapper").innerHTML = "okay done!";
}, function() {
    
});

document.getElementById("wrapper").innerHTML = "i will be disappeared!";