[JS] Add examples of prototypal inheritance (#202)

questions/javascript-questions.md

@@ -99,10 +99,84 @@ ES6 allows you to use [arrow functions](http://2ality.com/2017/12/alternate-this
 
 This is an extremely common JavaScript interview question. All JavaScript objects have a `prototype` property, that is a reference to another object. When a property is accessed on an object and if the property is not found on that object, the JavaScript engine looks at the object's `prototype`, and the `prototype`'s `prototype` and so on, until it finds the property defined on one of the `prototype`s or until it reaches the end of the prototype chain. This behavior simulates classical inheritance, but it is really more of [delegation than inheritance](https://davidwalsh.name/javascript-objects).
 
+#### Example of Prototypal Inheritance
+
+We already have a build-in `Object.create`, but if you were to provide a polyfill for it, that might look like:
+
+```javascript
+if (typeof Object.create !== 'function') {
+  Object.create = function (parent) {
+    function Tmp() {}
+    Tmp.prototype = parent;
+    return new Tmp();
+  };
+}
+
+const Parent = function() {
+  this.name = "Parent";
+}
+
+Parent.prototype.greet = function() { console.log("hello from Parent"); }
+
+const child = Object.create(Parent.prototype);
+
+child.cry = function() {
+  console.log("waaaaaahhhh!");
+}
+
+child.cry();
+// Outputs: waaaaaahhhh!
+
+child.greet();
+// Outputs: hello from Parent
+```
+
+Things to note are:
+
+* `.greet` is not defined on the _child_, so the engine goes up the prototype chain and finds `.greet` off the inherited from _Parent_.
+* We need to call `Object.create` in one of following ways for the prototype methods to be inherited:
+  * Object.create(Parent.prototype);
+  * Object.create(new Parent(null));
+  * Object.create(objLiteral);
+  * Currently, `child.constructor` is pointing to the `Parent`:
+
+```javascript
+child.constructor
+ƒ () {
+  this.name = "Parent";
+}
+child.constructor.name
+"Parent"
+```
+  * If we'd like to correct this, one option would be to do:
+
+```javascript
+function Child() {
+  Parent.call(this);
+  this.name = 'child';
+}
+
+Child.prototype = Parent.prototype;
+Child.prototype.constructor = Child;
+
+const c = new Child();
+
+c.cry();
+// Outputs: waaaaaahhhh!
+
+c.greet();
+// Outputs: hello from Parent
+
+c.constructor.name;
+// Outputs: "Child"
+```
+
 ###### References
 
 * https://www.quora.com/What-is-prototypal-inheritance/answer/Kyle-Simpson
 * https://davidwalsh.name/javascript-objects
+* https://crockford.com/javascript/prototypal.html
+* https://developer.mozilla.org/en-US/docs/Web/JavaScript/Inheritance_and_the_prototype_chain
 
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