What is difference between var,let and const;

VAR

It is a keyword for variable declaration in javascript. It is function scoped means if you declared a variable inside a block of a function then it is scoped to whole function not just inside the block . It's available for whole function doesn't matter you are using it before declaration because of hoisting. like this one

function greeting(waves){
if(waves===true){
   var greet= "Hello Champ!"
}

return greet;
}

but if you want access greet before if block it is accessible which would have value undefined because hoisting but what is hoisting ?

Hoisting

In hoisting if a variable is declared using var keyword then it hosted on top of the function just variable declaration not the value of the variable. like this one

function greeting(waves){
console.log(greet)
if(waves===true){
   var greet= "Hello Champ!"
}

return greet;
}

greeting(false)

LET

It is also a keyword for variable declaration in javascript. But it is block scoped means its available for that block only not outside that block. like this one

function greeting(waves){
if(waves===true){
   let greet= "Hello Champ!"
}

return greet;
}

greeting(false)

In this function if waves value is false then in that case it would give a error Uncaught ReferenceError: greet is not defined greet is only accessible in if block only not outside the block.

CONST

It is also a keyword for variable declaration but for constant value. It is also block scoped. And it value assigned only once in block.

Thanks for reading. Feel free to correct.