Ultimate JavaScript

Scope in JavaScript

Scope in JavaScript can call current context of execution .The context in which values and expressions are visible . We can imagine scope as a world .Every Scope as like a separate world .

JavaScript has a global scope in browser we can call it window scope

Let’s see a example :

var a=”20";

function(){

var b=”30"

}

console.log(a) //”20"

Here “a” is variable which in belongs to global scope

we can test with that

console.log(window.a) //”20"

##Parent Child Concept

Child can access variables of parent but parent can’t

and parent can change the value ass well

Let’s see:

var a=”20";

function(){

var a=”30"

}

console.log(a) //”30"

Execution Context

Execution context has two phase in JavaScript

1. Creation-al phase
2. Execution-al phase

Creation-al phase find out the declaration of variable and function store those things . For function this store reference id and for variable , definition of variable and set this value “undefined”

At Execution-al phase execute the function if this function is declare and for variable set actual value which is assign to variable

Var,Let And Const

Var is a function scope and let is a block scope

let’s see a example

function (){

for(var i=0;i<10;i++){

//something

}

for(let j=0;j<10;j++){

//something

}

console.log(i) //10

console.log(j) //undefined

}

#As let const is same but in const we cant refined his value

Primitive and reference data type

In short primitive type this data type is immutable

but reference type is mutable

— let’s see a example

let x=”ok”

const k={

g:”kalo”

}

x.toUpperCase()

console.log(x) // ok immutable

k.g=”alu”

console.log(k.g) //alu “mutable”

Try catch in JavaScript

We can handle error through try catch method in JavaScript

— -Syntax

try{

//try something to do

// if success then ignore catch error

}

catch{

// if fail to do then send error to user

}

Arrow Function

Arrow function introduced from ES6 is alternative for traditional function

— let’s see syntax

// Traditional Function
function aku(a){
  return a + 100;
}
// Arrow function
let aku=a=>a+100

Default value Function

Default value function allow named parameter to be initialize default value if no value is assign or undefined is pass

— let see example

function multiply(a, b = 1) {
return a * b;
}

function sum(a, b = 1) {
  return a + b;
}
console.log(sum(5, 2));
// expected output: 7
console.log(sum(5));
// expected output: 6

Rest operator

Rest operator allow function o accept an indefinite number of arguments as an array.

— Let’s See example

function allNum(a,  b, ...manyMoreArgs) {
  console.log("a", a)
  console.log("b", b)
  console.log("manyMoreArgs", manyMoreArgs)
}

allNum("one", "two", "three", "four", "five", "six")

// Console Output:
// a, one
// b, two
// manyMoreArgs, ["three", "four", "five", "six"]

Spread Syntax

Spread syntax can be used when all element of object or array need to include. We can use this for object cloning also

— let’s se example

const obj={
a:"a",
b:"b",
c:"c"
}
let objClone = { ...obj }; // pass all key:value pairs from an object

Block

A block statement use to group zero or more statements

—

{
  allstatements
}