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2016-02-17

Important concepts about Javascript for Node JS Developer

Special Values
Null,undefined,{},NaN,Infinity

Special Datatype
object,function,string,number

Typecase
parseInt(),parseFloat(),Boolean()

check datatype :
typeof()-return as string like 'number','object'
instanceof-[] instanceof Array=>true
isNaN(),isFinite()

String Functions:
length,indexOf(),substr(),slice(),split,trim(),search(REGULAR EXPR)

Create Object:
var obj1={first_name='manab',last_name='basu'}

delete properties from object:
delete user.first_name

to add properties in object :
user["first_name"]="Manab"

lenght Of Object
Object.keys(user).length

Array:
Create Array:var arr=[] or var arr=['a','b','c']
typeof arr=Object

Check : Array.isArray(arr)

Add Item: arr.push('a') or arr[4]='a' or arr.unshift('c')- add element at beginning

Delete Item-delete arr[3] or arr.pop()-pop item from the end,arr.shift()-Remove item from begening

Extract Element from array-arr.splice(START_INDEX,NO OF ELEMENT) & it reduce the array size based on NO OF ELEMENT

String to array:"A,b,c".split(',');

Array to string:[1,2,3].join(":");=>1:2:3

Sort:arr.sort()

Sort String of array(names):
names.sort(function(a, b){
var a1=a.toLowerCase(),b1=b.toLowerCase();
    if(a1 < b1) return -1;
    if(a1 > b1) return 1;
    return 0;
})

Functions:
check arguments:write- console.log(arguments);- within function

Constraint
Ternary Operator: var x=today?"X":"Y"

prototype:The prototype property is initially an empty object, and can have members added to it - as you would any other object.
var myObject = function(name){
    this.name = name;
    return this;
};
console.log(typeof myObject.prototype); // object
myObject.prototype.getName = function(){//adding a new member getName() to the class myObject
    return this.name;
};
or
function Shape(){
};
Shape.prototype.X=0;
Shape.prototype.Y=0;
Shape.prototype.move=function(x,y){
 this.X=x;
 this.Y=y;
}
Shape.prototype.distance=function(){
 return Math.sqrt(this.X*this.X+this.Y*this.Y);
}
//call
var s=new Shape();
s.move(10,10);
console.log(s.distance());

Inheritance:
function Square(){}
Square.prototype=new Shape();
Square.prototype.__proto__=Shape().prototype;
Square.prototype.width=0;
Square.prototype.area=function(){
 return this.width*this.width;
}
var sq=new Square();
sq.move(5,5);
sq.width=15;
console.log(sq.distance());
console.log(sq.area());
Error Handling:
function test(){
 throw new Error("Bad Error");
}
//Calling Function
try{
 test();
}
catch(e){
 console.log(e.message);
}
Global: global object
global.name="Manab";
global["name"];

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