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difference between var, let, const

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Md. Asif Iqbal answered on August 17, 2020 Popularity 10/10 Helpfulness 2/10

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difference between var, let, const

Comment

// var is a function scope ***
if(true){
    var varVariable = 'This is var';
    var varVariable = 'This is var again';
}

console.log(varVariable); // This is var again

// let is a block scope ***
if(true){
    let letVariable = 'This is let';
    let letVariable = 'This is let again';

    // let variable can't re-define but we can re-assign value


    console.log(letVariable); // let letVariable = 'This is let again';^SyntaxError: Identifier 'letVariable' has already been declared
}

console.log(letVariable); //ReferenceError: letVariable is not defined



// const variable can't re-define and re-assign value
// const is a block scope ***
if(true){
    const constVarible = {
        name: 'JavaScript',
        age: '25 years',
    };
    constVarible.name = 'JS';

    console.log(constVarible) // {name: 'JS',age: '25 years'} <= we can update const variable declared object 
}

Popularity 10/10 Helpfulness 2/10 Language javascript

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Contributed on Sep 13 2021

Md. Asif Iqbal

0 Answers Avg Quality 2/10

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var vs let vs const

Comment

var: 
	- hoisted (always declared at top of scope, global if none)
    - function scope
let:
    - block scope
    - not redeclarable
const: 
    - block scope
    - not reassignable
    - not redeclarable
    
Note: Although it may seem like these hold only semantic meaning, using the
appropriate keywords helps the JS engines' compiler to decide on what to optimize.

Popularity 10/10 Helpfulness 6/10 Language whatever

Source: Grepper

Tags: let

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Contributed on May 11 2021

GitPaulo

0 Answers Avg Quality 2/10

difference between var and let

Comment

var is function scoped and let is block scoped. Let's say you have:
function understanding_var() {
	if (1 == 1) {
    	var x = 5;
        console.log('the value of x inside the if statement is ' + x);
    }
    console.log(x);
} 
//output: the value of x inside the if statement is 5
		  5

function understanding_let() {
	if (1 == 1) {
    	let x = 5;
        console.log('the value of x inside the if statement is ' + x);
    }
    console.log(x);
} 
//output: the value of x inside the if statement is 5
		  Uncaught ReferenceError: x is not defined
          
var is defined throughout the entire function, even if it's inside the if 
statement, but the scope of let is always within the curly braces, not outside
it, even if the conditional statement is inside the function.

Popularity 10/10 Helpfulness 4/10 Language javascript

Source: Grepper

Tags: between

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Contributed on Nov 27 2020

Important Ibex

0 Answers Avg Quality 2/10

let vs const

Comment

`const` is a signal that the identifier won't be reassigned.

`let` is a signal that the variable may be reassigned, such as a counter in a
loop, or a value swap in an algorithm.

It also signals that the variable will be used only in the block it's defined
in, which is not always the entire containing function.

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Contributed on Aug 17 2020

Fylls

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diff between let var const

Comment

Difference between let var const
	
	Var, Let, Const keywords introduced in ES6 (2015).
	1] Var:
		Var can reassign value
		Var can have global or local scope
	2] Let:
		Let can not be redeclared.
		Let have block scope.
		Let can reassign value
	3] Const:
		Const cannot be Redeclared.
		Const cannot be Reassigned.
		Const have Block Scope.

Popularity 10/10 Helpfulness 3/10 Language javascript

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Tags: between

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Contributed on Mar 31 2023

@CodeGrepperManu

0 Answers Avg Quality 2/10

difference between var, let, const

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