JavaScript

https://developer.mozilla.org/en-US/docs/Web/JavaScript https://developer.mozilla.org/en-US/docs/Learn/Getting_started_with_the_web/JavaScript_basics

LightWeight - easy to implement
Interpreted - No Compilation
Object Oriented
First class function - Functions as value 5.Scripting Language

Why Js? To Rich Web Dev . Native JS . Framework . Angular JS, React JS, Ember Server Side . Node Js

ECMA Script - Spec for Javascript latest ECMA script ES6

Variable

No Typed Variable var myVariable;

Type: String Number Boolean Array ex: var myVar = [10,'Sasi',true] undefined (absence of value) Object ,null (special value indicated for non value) Middle Name Example

Mix and Match: //Loose Typing var a =10; a='Hello'

Decleration(declare variable) and Definition(assign Value)

OPERATOR

typeof - gives dataType

if Condition

Values of all types have an associated boolean value

False Conditions if(0) console.log('hi'); else console.log('Hello'); //Hello if("") console.log('hi'); else console.log('Hello'); //Hello if(null) console.log('hi'); else console.log('Hello'); //Hello if(undefined) console.log('hi'); else console.log('Hello'); //Hello

True Conditions if(1) console.log('hi'); else console.log('Hello'); //Hi if("a") console.log('hi'); else console.log('Hello'); //Hi

Objects

JS objects are not class based objects. Object Consist of property and functions. Consider them as MAP with [k,v]

Ex: var myObj = {} // Creation Objects

Adding property

myObj.prop = 'Hello'; myObj.prop1 = 1; myObj.1 = 1;

Reading propety from Obj

Dot Notation

console.log(myObj.prop); console.log(myObj['prop']); console.log(myObj.1);//error

square bracket Notation - use this when key is reserved word and dynamic [optimization is less compared to Dot Notation]

console.log(myObj['prop']); console.log(myObj['1']); var propName = 'prop'; console.log(myObj[propName]);

#Nested Objects

var myObj = { prop1 : 1, prop2 : true, prop3 : 'hello', prop4 : { innerProp1 : 'innerProp' } }; myObj.prop4.newInnerProp = 'new inner prop'; console.log(myObj.prop4.innerProp1); console.log(myObj.prop4['innerProp1']); // min and match console.log(myObj.prop4.newInnerProp);

How === works with Object?
How undefined and null works with Object?
Can I assign undefined to variable decalred?

#Remove Object Property

delete myObj.prop1

#Arrays

var myArr = [1,2,3]

Access array - index zero based

console.log(myArr[0]);// 1

Add data to array

myArr[3] = 4; console.log(myArr[3]);// 4

Find the length of an array console.log(myArr.length) //4

Note : Array internally is a JS Object. See the console.log(myArr); Just like JS Object we can have nested Arrays. Even you can use myArr["0"] just like Objects.

myArr[400] = "Hi" console.log(myArr.length) //401 coz not the count of the element present. lenght is maxIndex + 1

myArr["newProp"] = "new prop"; console.log(myArr); // will it work?, Yes it works at Arrays are object Note: treat Arrays as arrays not as Objects

#Wrapper Objects

var myObj = "Hello";

console.log(myObj.length) // 5. How is this possible myObj typeOf is string. but we use dot notation like a object. it uses a wrapper Object(String) for fraction of second and convert it back to primitive

Number | Boolean

String | Symbol

#Functions -Function Delaraction function greet(){ console.log('Hello') }

. Syntax . Arguments - passing arguments are optional

function greet(fName,lName){ return 'Hello' + fName + lName; }

console.log(greet('Sasi')); Guess What?

. return Statment -

Example

function greet(){ return 'Hello'; }

console.log(greet());

function greet(){ return; }

console.log(greet()); Guess What?

#Function Expression - function itself is an value in JavaScript

var f = function greet(){ console.log('Hello'); } f(); // Hello;

what Happens to the below example var f = function greet(){ return function(){ return 'Hello'; } }

console.log(f()());

What are the ways in which you can create an function?

Function Delaraction - Function Expression

#Anonymous Function Expression var f = function(){ console.log('Hello'); } f(); // Hello;

#Function As Arugument

Ex1: var print = function(){ console.log('Hello'); }

var executor = function(fn){ fn(); } executor(print); // Hello;

Ex2: var print = function(name){ console.log('Hello '+name); }

var executor = function(fn,name){ fn(name); } executor(print,'Sasi'); // Hello;

#Function inside Object

Ex: var myObj = { prop1 : 1 }

myObj.myFn = function(){ console.log('new function'); }

myObj.myFn(); //prints new function

#this Keyword in functions var person = { fname : 'Sasi', lname : 'Kumar', getFullName : function(){ return person.fname + " " + person.lname; } };

console.log(person.getFullName()); // output??

var person2 = person;

console.log(person2.getFullName()); // output??

person = {}

console.log(person2.getFullName()); // output??

Excercise

var person = { fname : 'Sasi', lname : 'Kumar', getFullName : function(){ return person.fname + " " + person.lname; }, address : { street: '12123 st', city : 'Chennai', state : 'TN' }, isFromState : //Write a function that says if the person is from the state we are passing };

console.log(person.isFromState('TN'));

#Default function arguments -- get 2 args for free arguments,this

var add = function(a,b){ console.log(arguments) console.log(a+b) }

add(10,20,30);