javascript – ecmascript basics by satyen

8/7/2019 JavaScript – ECMAScript Basics By Satyen

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By: Satyen Pandya

1

JavaScriptJavaScript ECMAScript BasicsECMAScript Basics

[email protected]@gmail.com



ContentsContents

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Syntax, Variables, Keywords, Reserved Words

Primitive and Reference Values

Primitive Types

Conversions

Reference Types

Operators

Statements

Functions




SyntaxSyntax

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ECMAScript basic concepts :

Everything is case-sensitive

Variables are loosely typed

End-of-line semicolons are optional

Comments are the same as in Java, C, Perl

Braces indicate code blocks




VariablesVariables

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Variables are defined by var operator Variables do not require initialization like JAVA Variables can hold different types of values at

different times

Variable name First character must be letter, an underscore (_)\

or dollar sign ($) Remaining characters may be underscores, dollar

sings or any alphanumeric characters

Variable should follow Camel Notation (e.g. myTest, myVar) Pascal Notation (e.g. MyTest, MyVar) Hungarian Type Notation (e.g. sMyTest, bMyVar)




KeywordsKeywords

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Keyword used to indicate beginning and/or ending

of statements

Keywords are reserved, can not use as variable

or function name

Few Keywords :

break do in thow

case else instanceof typeof

catch finally new var

continue for return void

default function switch while

delete if this with

try




Reserved WordsReserved Words

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Word that are reserved for future use as keyword

Can not use as variable or function name

Few Reserved words :

abstrct enum int short

boolean export interface static

byte extends long super

char final native synchronized

class float package throws

const goto private transient

debugger implements protected Volatile

double import public




Primitive and Reference ValuesPrimitive and Reference Values

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Primitive values - simple piece of data, stored on stack,

the value is stored directly in location that variable

accesses

Reference values - objects, stored in heap, the value is

stored in variable location pointer, where the object

is stored




Primitive TypesPrimitive Types

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ECMAScript has five primitive types :

Undefined, Null, Boolean, Number, String

typeof Operator used to determine the type variables

value

typeof Operator takes one argument

typeof returns one of below value :

undefined, boolean, number, string, object




ConversionsConversions

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Type conversion is a short, one-step process in

ECMAScript

Converting to a string : var.toString()

Converting to a number :

var a = parseInt(123);

var b = parseFloat(123.456);

Type Casting :

Boolean(value);

Number(value);String(value);




Reference TypesReference Types

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They are referred as class, when you have a reference

value, you are dealing with an object

Objects are created by new operator and class name

e.g. var obj = new Object();

Few classes :

1. The Object class

2. The Boolean class

3. The Number class

4. The String class5. The instanceof operator




Reference Types (Contd)Reference Types (Contd)

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The object class : base class for all ECMAScript classes

All the properties and methods of Object class also

present in other classes

Properties :

constructor

Prototype

Methods :

hasOwnProperty(property)

isPrototypeof(object) propertyIsEnumerable(property)

toString()

valueOf()





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The Boolean class : reference type for Boolean type

pass only Boolean value

toString() returns true or false

valueOf() returns true or false

The Number class : reference type for Number type


toString() returns number primitive value

valueOf() returns number primitive value toFixed() returns string representation of number

toExponential returns e-notation string

toPrecision returns fixed or e-notation of number





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The String class : reference type for String type


toString() returns string primitive value

valueOf() returns string primitive value

length gives number of characters

charAt() returns string containing character in position

charCodeAt() returns character code

concat() concate two or more strings

indexOf() returns position of given substring lastindexOf() returns last position of given substring

The instanceof operator : identifies the type of object




OperatorsOperators

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Unary operators :

delete erases reference to an object property or

method

void returns undefined for any value

prefix increment/decrement (e.g. ++a, --a)

postfix increment/decrement (e.g. a++, a--)

unary plus returns exact same value for integer, for

string it converts them to numbers

unary minus returns negative value for integer, forstring it negates the value




Operators (Contd)Operators (Contd)

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Bitwise operators :

Bitwise NOT tilde(~), it works in 3 stpes

1. Operand is converted to 32-bit number

2. Binary form converted into its ones complement

3. Ones complement is converted back to number

Bitwise AND ampersand(&)

works directly on the binary form of numbers

Bitwise OR pipe(|)

works directly on the binary form of numbers Bitwise XOR caret(^)

works directly on the binary form of numbers





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Bitwise operators :

Bit from FirstNumber Bit from SecondNumber A & B A | B A ^ B

1 1 1 1 0

1 0 0 1 1

0 1 0 1 1

0 0 1 0 0





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Boolean operators :

Logical NOT exclamation(!), always return Boolean

Logical AND double ampersand(&&)

Logical OR double pipe(||)

Operand 1 Operand 2 A && B A || B

true true true true

true false false truefalse true false true

false false false false




Multiplicative operatorsMultiplicative operators

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Multiply : represented by asterisk(*)

Divide : represented by slash(/)

Modulus : represented by percent sign(%)

Additive operatorsAdditive operators

Add : represented by plus(+) Subtract : represented by minus(-)

Modulus : represented by percent sign(%)




Relational operatorsRelational operators

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less-than : represented by <

greater-than : represented by >

less-than-or-equal : represented by <=

greater-than-or-equal : represented by >=

Equality operatorsEquality operators

Equal : represented by double equal sign (==)

Not Equal : represented by exclamation with equal sign

(!=)

Identically equal : three equal sign (===)

Not identically equal : exclamation and two equal (!==)




Conditional operatorsConditional operators

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Syntax :Variable = boolean_expression ? true_value : false_value;

if expression is true then true_value will be assigned,

else false_value will be assigned

Assignment operatorsAssignment operators Simple assignment operator (=) assings the value on the

right to the variable on the left

Comma operatorsComma operators

more than one operation in single line




Thank youThank you

By: Satyen Pandya


javascript – ecmascript basics by satyen

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