Java Script Introduction

JavaScript Introduction Aaron Conran Text: JavaScript The Definitive Guide By David Flannagan

Case Sensitive

Example:

myVar

myVAr

These are not the same variable.

(Optional) Semicolons

JavaScript allows you to omit semicolons at the end of your statements.

However this can create nasty bugs and cause difficult to debug problems.

Use them at the end of statements and make your life easier.

Comments

JavaScript supports both C and C++ style comments

// this is a comment

/* this is another comment */

Comments (JSDoc)

Comments which begin with /**

Note the 2 stars will be picked up by JSDoc

JSDoc allows you to document your JavaScript classes in a formal manner similar to JavaDoc.

Allows code and documentation to always be synchronized.

For more information:

http://jsdoc.sourceforge.net/

JavaScript Reserved Words

Avoid the use of reserved words as variables and function names in your JavaScript.

For a full list

Flanagan p19-20

Examples:

break

if

switch

in

class

JavaScript DataTypes

Numbers

Strings

Booleans

Functions

Objects

Arrays

null

undefined

Date

Error

Numbers

Integer (whole)

Hexadecimal & Octal

Floating-points (decimal)

You can add, multiply divide and subtract numbers with their respective operator: +, *, /, & -

The Math library of JavaScript also exposes a number of useful methods:

Math.abs(num)

Math.sin(num)

Math.ceil(num)

Full reference p 659-669

Special Numeric Values (Table 3-1) p25 Special value to represent negative infinity Number.NEGATIVE_INFINITY Special value to represent infinity Number.POSTIVE_INFINITY Special not a number value Number.NaN Smallest (closest to zero) representable number Number.MIN_VALUE Largest representable number Number.MAX_VALUE Special not-a-number value NaN Special value to represent infinity Infinity Meaning Constant

Strings

“ zero or more Unicode characters enclosed within single or double quotes”

Examples:

“”

‘ myForm’

“ testing”

“ This is a longer string”

Escape Sequences

To encode special values like new lines and ‘s in JavaScript strings you utilize a backslash

Example:

var menuText = ‘What’s this?’;

Escape Sequences (Table 3-2) p27 The Latin-1 character specified by the octal digits XXX, between 1 and 377. Not support by ECMAScript v3; do not use this escpae sequence. XXX The Unicode character specified by the four hexadecimal digits XXXX uXXXX The Latin-1 character specified by the two hexadecimal digits XX xXX Backslash (u005C) \ Apostrophe or single quote (u027) ’ Double quote (u022) ” Carriage return (u00D) Form feed (u000C) f Vertical tab (u000B) v Newline (u000A) Horizontal tab (u0009) Backspace (u0008) The NUL character (u0000) Character represented Sequence

Adding Strings

You can also add (or concatenate) strings simply by adding them.

Example:

var anotherString = ‘new’;

var newVariable = ‘Something ‘ + anotherString;

When adding numbers they will automatically be converting to strings.

Example:

var x = 12;

var newString = x + ‘ dozen eggs’;

Converting Strings To Numbers

Utilize the parse Number utility functions to extract numbers from strings.

parseInt

parseFloat

Example:

var x = “11”;

var xNum = parseInt(x);

Booleans

true

(Other truthy values)

1

{}

‘ ‘ - space

‘ my String’

false

(Other falsey values)

undefined

null

0

“” – empty string

Equals vs Strictly Equals

There is a strictly equals operator in JavaScript which will also check type as well as value. To show how this relates to boolean values:

== Equals

Works for Truthy values

=== Strictly Equals

Works for truth only

!= Not Equals

Works for Falsey values

!== Strictly Not Equals

Works for false only

Objects

JavaScript Objects are similar to ColdFusion Structures.

They consist of zero to many key-value pairs.

They can be nested infinitely deep.

They provide an associative array or hash map.

Example:

// using the Object constructor

var newObj = new Object();

newObj.x = 10;

newObj.y = 20;

// OR using the Object literal syntax

var newObj = {x: 10, y: 20};

Object Literal

Object literal is the preferred way to create objects because it is concise and consistent with JSON-syntax.

When utilizing object literal syntax key value pairs are separated by colon’s.

Keys are called properties

Functions

Functions are actually a datatype too

Example:

var myFn = function() {console.log(‘hi’);};

function myFn() {console.log(‘hi’);}

These are 2 different ways of defining a similar function. There is also a Function constructor, however it’s use is limited because it can only create functions in the global scope.

Functions as Properties

Properties of Objects can be any data type including Functions.

Example:

var myObject = {myFun: function() {console.log(‘hi’);}};

myObject.myFun();

Arrays

Arrays can be defined using 2 syntaxes as well.

Example:

// Utilizing the Array constructor

var myArray = new Array();

myArray[0] = 12;

myArray[1] = 232;

// OR using the Array literal syntax.

var myArray = [12,232];

Arrays (cont.)

Arrays can be infinitely nested

Arrays can be sparse

Arrays can store unlike datatypes

Full reference available p 602-611

Arrays provide a number of useful properties and methods such as:

length – property which defines how many elements are in the Array

push – method which pushes another element on the Array when utilized as a Stack

pop – method which pops an element off an Array when utilized as a Stack

null vs undefined

null

“ null is a special keyword which indicates no value”

undefined

“ undefined is returned when you use either a variable that has not been declared but never had a value assigned to it or an object property that does not exist”

null vs undefined