Interview question

What is the difference between function declaration and function expression? Function declaration और function expression में क्या अंतर है?

Answer

Aspect	Declaration	Expression
Syntax	function name() { }	const name = function() { }
Hoisting	Fully hoisted - can call before declaration	Not hoisted - throws error if called before
Named	Always named	Can be anonymous or named
When it runs	At parse time	At runtime

// Function Declaration - hoisted
console.log(greet1()); // 'Hello' - works!
function greet1() {
    return 'Hello';
}

// Function Expression - not hoisted
console.log(greet2()); // ReferenceError: Cannot access 'greet2' before initialization
const greet2 = function() {
    return 'Hello';
};

// Named function expression
const factorial = function fact(n) {
    return n <= 1 ? 1 : n * fact(n - 1);
};

Interview tip: Explain that hoisting means function declarations are moved to the top of their scope at parse time, but function expressions are only initialized when the code runs. This is a common source of bugs.

Aspect	Declaration	Expression
Syntax	function name() { }	const name = function() { }
Hoisting	Fully hoisted - पहले call कर सकते हैं	Hoisted नहीं - error मिलेगी
Named	हमेशा named	Anonymous या named
Execution	Parse time पर	Runtime पर

// Declaration - hoisted
console.log(greet1()); // 'Hello' - काम करता है!
function greet1() {
    return 'Hello';
}

// Expression - hoisted नहीं
console.log(greet2()); // ReferenceError
const greet2 = function() {
    return 'Hello';
};

// Named function expression
const factorial = function fact(n) {
    return n <= 1 ? 1 : n * fact(n - 1);
};

इंटरव्यू टिप: समझाएं hoisting का मतलब function declarations को scope के top पर move किया जाता है, पर function expressions सिर्फ तब initialize होते हैं जब code run हो।

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