Interview question

What are the differences between var, let, and const in JavaScript? JavaScript में var, let और const में क्या अंतर है?

Answer

Keyword	Scope	Hoisting	Re-declaration	Re-assignment
var	Function-scoped	Hoisted, initialized as undefined	Yes	Yes
let	Block-scoped	Hoisted but not initialized (TDZ)	No	Yes
const	Block-scoped	Hoisted but not initialized (TDZ)	No	No

function test() {
    console.log(x); // undefined (hoisting)
    var x = 1;
    
    if (true) {
        let y = 2;  // block-scoped
        const z = 3; // block-scoped, can't be reassigned
    }
    console.log(y); // ReferenceError: y is not defined
}

Interview tip: Always use const by default, let if reassignment needed, and avoid var. Mention Temporal Dead Zone (TDZ) for let/const.

Keyword	Scope	Hoisting	Re-declaration	Re-assignment
var	Function-scoped	Hoisted, undefined	हाँ	हाँ
let	Block-scoped	Hoisted नहीं (TDZ)	नहीं	हाँ
const	Block-scoped	Hoisted नहीं (TDZ)	नहीं	नहीं

function test() {
    console.log(x); // undefined (hoisting)
    var x = 1;
    
    if (true) {
        let y = 2;  // block-scoped
        const z = 3; // block-scoped
    }
    console.log(y); // ReferenceError
}

इंटरव्यू टिप: Default const use करें, reassignment चाहिए तो let, var से बचें। Temporal Dead Zone (TDZ) का ज़िक्र करें।

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