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javascriptvariablesinitializationdeclarelet
monkeDB
monkeDB

Reputation: 21

Javascript var/let/const variable initialization

Javascript novice here. From https://www.freecodecamp.org/news/var-let-and-const-whats-the-difference/ :

So "const" is clear that it's initialized as the value it was originally declared as.

"var":

a) not declared, initialized as undefined
b) declared, initialized accordingly

"let":

a) not declared, initialized as ______???______
b) declared, initialized accordingly

What is "let" initialized as if it's not declared at first?

Upvotes: 2

Views: 3530

Answers (3)

Sirode
Sirode

Reputation: 597

Well, the easiest way to think about it is that there is only 1 type of undeclared variable (in the sense of never declared, otherwise you just get a ReferrenceError). If it is never declared, the JavaScript engine can't be choosing to make it a var or a let or a const to fit the developer needs.

Any never declared variable that is assigned a value becomes a global scope variable (ref: comment from Avikalp Gupta)

Upvotes: 0

georg
georg

Reputation: 215059

Hoisted let variables are initialized with a special "value" that throws a ReferenceError when accessed:

function foo() {
    console.log(x)  // ReferenceError: Cannot access 'x' before initialization
    let x
}

foo()

let and const declarations define variables that are scoped to the running execution context's LexicalEnvironment. The variables ... may not be accessed in any way until the variable's LexicalBinding is evaluated.

https://tc39.es/ecma262/multipage/ecmascript-language-statements-and-declarations.html#sec-let-and-const-declarations

Upvotes: 0

Satyapriya Raut
Satyapriya Raut

Reputation: 9

let if declared and not initialized, then its default value is set to undefined.

let x;
console.log(x);

>> undefined

Upvotes: 1

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