Some Important Topics Of JavaScript

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Truthy and falsy Values

When values are set to True, it’s truthy otherwise false. There are only six values are falsy and rest are considered as truthy values.

• false
• undefined
• null
• “”
• NaN
• 0

“null vs undefined”

“null” is a value which is assigned to a variable. It represents no value as a result. But, undefined is a variable type and null is an object.

let x = null;
console.log(x);
//null

You can think undefined as simply that you declared a variable but not defined this.

let x ;
console.log(x);
//undefiend

In spite of some similarities like both are falsy and primitive values, null and undefined is not strictly the same.

var sum1 = 5+ null;
console.log(sum1)
//5
var sum2 = 5+ undefined;
console.log(sum2)
//NaN

so, null !==undefined but null == undefined

Double equal (==) and Triple equal(===)

Double equal (==) is used to compare two variables, it ignores data types. On the other side, triple equal (===) is used to compare not only values but also data types.

const num = 3183; 
const numString = '3183';  

console.log(num == numString) //true
console.log(num === numString)  //false

Implicit Conversion

It’s a popular feature in javascript. When you needed to convert an unexpected value type to the expected value type, you can use it.

1 + "3" + 1 //131
true + true //2
1 - true //0

Scope in Javascript

Scope helps to determine the visibility of variables. There are two scopes in javascript like global and local. when we declare a variable as a global, we can call it from anywhere in code. But when we declare a variable as a local in a function, we can use it only inside this function.

var name = 'java';

console.log(name); // 'java'

function showName() {
   var name = 'python';
   console.log(name); // 'python'
}

console.log(name) //'java'

Block Statement

It’s like if and switch condition. It does not create scope like functions.

if(true){
var name = "jhon";
var age = "33";
}
console.log(name) //'jhon'
console.log(age) //33

“new” keyword in JavaScript

“new” keyword creates a new object. So, the type of it is an object. It modifies “this” and returns the value of “this”.

function Student (name){
this.name = name;
}
let person = new Student("luffy")
console.log(person.name);

Thank you!