JavaScript Patterns 1 Introduction

1.1 Pattern

"theme of recurring events or objects… it can be a template or model which can be used to generate things" (http://en.wikipedia.org/wiki/Pattern).

• Design patterns - Elements of Reusable Object-Oriented Software.

• Coding patterns - JavaScript-specific patterns and good practices related to the unique features of the language, such as the various uses of functions.

• Antipatterns - An antipattern is not the same as a bug or a coding error; it's just a common approach that causes more problems than it solves.

1.2 JavaScript: Concepts

None-Objects: Primitive types - number, string, boolean, null, and undefined

1.2.1 Object- Oriented

Activation Object which is a global object which has attributes.

Object: a collection of named properties, a list of key-value pairs. Some properties could be functions.

Objects types

1. Native

   Described in the ECMAScript standard

2. Host

   Defined by the host environment (for example, the browser environment, e.g. window and all the DOM object) .

Objects can also be categorized by:

1. Build-in (e.g. Array, Date).
2. User-defined (e.g. var o ={}).

1.2.2 No Classes

There are no long parent-child inheritance chains.

There are no classes and object composition is what you do anyway.

1.2.3 Prototypes

prototype is an object (not a class or anything special) and every function has a prototype property.

1.2.4 Environment

1. Browser patterns
2. Practical applications of a pattern

1.3 ECMAScript 5

Strict mode - for backward compatible.

function my() {

"use strict";

// rest of the function...

}

This means the code in the function is executed in the strict subset of the language. For older browsers this is just a string not assigned to any variable, so it's not used, and yet it's not an error.

In this sense ES5 is a transitional version—developers are encouraged, but not forced, to write code that works in strict mode.

Principle on writing code under strict mode

• Ensuring the offered code samples will not raise errors in strict mode

• Avoiding and pointing out deprecated constructs such as arguments.callee

• Calling out ES3 patterns that have ES5 built-in equivalents such as Object.create()

1.4 JSLint - A kind of tool for grammar check.

1.5 The console - fire bug