My Notes from Pro JavaScript Design Patterns

1
2Function.prototype.method = function(name, fn) { this.prototype[name] = fn; }
3
4var Anim = function() {}
5Anim.method('start', function() {
6  ....
7})
8
9Anim.method('close', function() {
10  ....
11})
12

1
2// This version allows the calls to be chained together
3
4Function.prototype.method = function(name, fn) {
5this.prototype[name] = fn;
6return this;
7}
8

1
2var myObject = {
3value: 0,
4increment: function(inc) {
5this.value += typeof inc === 'number' ? inc : 1;
6}
7}
8
9myObject.increment();
10console.log(myObject.value); // 1
11

1
2function displayError(message) {
3displayError.numTimesExecuted++;
4console.log(message);
5}
6
7displayError.numTimesExecuted = 0;
8

1
2function Person(name, age) {
3this.name = name;
4this.age = age;
5}
6
7Person.prototype.sayName = function() {
8console.log(this.name);
9}
10
11Person.prototype = {
12getName: function() {
13return this.name;
14},
15getAge: function() {
16return this.age;
17}
18}
19
20var alice = new Person('John', 30);
21var bill = new Person('Bill', 40);
22person.sayName();
23
24bill.displayGreeting = function() {
25console.log('Hello, I am ' + this.name);
26}
27
28bill.displayGreeting();
29
30// This example shows that you can add properties to an object after it has been created.
31// Also just bill has the displayGreeting method, alice does not.
32

1
2
3/*
4interface Composite {
5function add(child);
6function remove(child);
7function getChild(index);
8}
9
10interface FormItem {
11function save();
12}
13
14*/
15
16var CompositeForm = function(id, method, action) { // implements Composite, FormItem
17....
18}
19
20// Implement the Composite interface
21
22CompositeForm.prototype.add = function(child) {
23....
24}
25
26CompositeForm.prototype.remove = function(child) {
27....
28}
29
30CompositeForm.prototype.getChild = function(index) {
31....
32}
33
34// Implement the FormItem interface
35
36CompositeForm.prototype.save = function() {
37....
38}
39
40// This doesn't emulate the interface functionality very well. There is no checking to ensure that CompositeForm implements the methods defined in the interface.
41// No error will be thrown if you forget to implement a method.
42

1
2
3/*
4interface Composite {
5function add(child);
6function remove(child);
7function getChild(index);
8}
9
10interface FormItem {
11function save();
12}
13*/
14
15var CompositeForm = function(id, method, action) {
16this.implementsInterfaces = ['Composite', 'FormItem'];
17...
18}
19....
20
21function addForm(formInstance) {
22if (!implements(formInstance, 'Composite', 'FormItem')) {
23throw new Error('Object does not implement a required interface.');
24}
25}
26
27
28
29// This is a better way to emulate interfaces. The addForm function checks to make sure that the object passed in implements the required interfaces.
30// The CompositeForm constructor also checks to make sure that the object implements the required interfaces.
31
32function implements(object) {
33for(var i = 1; i < arguments.length; i++) {
34var interfaceName = arguments[i];
35var interfaceFound = false;
36
37for(var j = 0; j < object.implementsInterfaces.length; j++) {
38  if(object.implementsInterfaces[j] == interfaceName) {
39    interfaceFound = true;
40    break;
41  }
42}
43
44if(!interfaceFound) {
45  return false; // An interface was not found.
46}
47}
48
49return true; // All interface were found.
50}
51

1
2
3var Composite = new Interface('Composite', ['add', 'remove', 'getChild']);
4var FormItem = new Interface('FormItem', ['save']);
5
6// CompositeForm class
7
8var CompositeForm = function(id, method, action) {
9...
10}
11
12....
13
14fucntion addForm(formInstance) {
15ensureImplements(formInstance, Composite, FormItem);
16// This function will throw an error if the object passed in does not implement the required interfaces.
17...
18}
19

1
2
3// Interfaces - Defines interface as commands to check for their existence.
4
5var Composite = new Interface('Composite', ['add', 'remove', 'getChild']);
6var FormItem = new Interface('FormItem', ['save']);
7
8// CompositeForm class
9
10var CompositeForm = function(id, method, action) {
11...
12}
13
14....
15
16fucntion addForm(formInstance) {
17Interface.ensureImplements(formInstance, Composite, FormItem);
18// This function will throw an error if the object passed in does not implement the required interfaces.
19// All code beneath this line will be executed only if the checks pass.
20...
21}
22// Interface.ensureImplements provides a strict check. If a problem is found, an error will be thrown, which can either be caught and handled or alllowed to halt execution.
23// Either way, the problem will be found and fixed.
24
25

1
2
3// Interface.js - Defines Interface constructor.
4
5var Interface = function(name, methods) {
6if(arguments.length != 2) {
7throw new Error('Interface constructor called with ' + arguments.length + 'arguments, but expected exactly 2.');
8}
9
10this.name = name;
11this.methods = methods;
12
13for(var i = 0, len = methods.length; i < len; i++) {
14if(tpeof methods[i] !== 'string') {
15  throw new Error('Interface constructor expects method names to be passed in as a string.');
16}
17this.methods.push(methods[i]);
18}
19}
20
21// Static class method.
22
23Interface.ensureImplements = function(object) {
24if(arguments.length < 2) {
25throw new Error("Function Interface.ensureImplemtns called with" + arguments.length + "arguments, but expected at least 2.");
26}
27
28for(var i = 1, len = arguments.length; i < len; i++) {
29var interface = arguments[i];
30if(interface.constructor !== Interface) {
31  throw new Error("Function Interface.ensureImplements expects arguments" + "two and above to be instancs instaces of Interface.");;
32}
33
34for(var j = 0; methodsLen = interface.method.length; j < methodsLen; j++) {
35  var methods = interface.methods[j];
36  if(!object[methods] || typeof object[methods] !== 'function') {
37    throw new Error("Function Interface.ensureImplements: object" + "does not implement the " + interface.name + " interface. Method " + methods + " was not found.");
38  }
39}
40}
41}
42
43