JavaScript Core Concept

3 min readMay 8, 2021

JavaScript Truty and Falsy: In javaScript, if/else statement check true or false condition. if the condition is true then return a true value otherwise false. we see some example below:

When we are using number value in if/else condition for check result is true or false. if we are using 0 in condition then return false otherwise return true at list without 0 number everything return number true in number value. Example below.

// Falsy value// 0, -0, '', false, null, undefiend, NaN

Null vs Undefined: Undefined and Null closely same but they are different in form. This article will explore the difference between null and undefined. Let’s start.

Undefined: Undefined means if we don't define anything or don't declare any variable value that's return undefined. We get undefined like 6 to 7 way. Example below:

let names;
condole.log(names)// except output: undefined// there is dont't return anyting therefore return undifiendfunction sum(num1, num2){   }
 const output = sum(12, 22)
 console.log(output);

If we declare an object and declare some property and value. there are we create a student object and have to property name, roll if we want to read sub property value from an object that returns an undefined value. Example below:

Null: Usually null is empty or non-existing value & need to defined value null that’s return null.

const name = null;
condole.log(name) // except output: null

Diffarence between == or === :

(==) means Abstract Equality Comparison. Usually == compare two values are after converting both values to a common type. == don’t care of value type. An example below:

And (===) Strict Equality comparison. Usually, compare two values. === take extra-care of values type if value type is different this return unequal. if values are the same type and same value they return equal.