Interview question

What is the difference between null and undefined in JavaScript? JavaScript में null और undefined में क्या अंतर है?

Answer

Aspect	null	undefined
Type	Object (due to a bug)	undefined
Meaning	Intentional absence of a value	Unintentional absence of a value
When assigned	By programmer explicitly	By JavaScript automatically
Examples	let x = null;	let x; or function(param) { }

// undefined
let a;  // declared but not assigned
console.log(a); // undefined

function test(param) {
    console.log(param); // undefined if not passed
}
test();

// null
let b = null;  // explicitly assigned
console.log(b); // null

// Comparison
console.log(null == undefined);   // true (loose equality)
console.log(null === undefined);  // false (strict equality)
console.log(typeof null);         // 'object' (famous bug!)
console.log(typeof undefined);    // 'undefined'

Interview tip: Explain that null is intentional (developer sets it) while undefined is unintentional (JavaScript sets it). Also mention the famous bug: typeof null === 'object'.

Aspect	null	undefined
Type	Object (एक bug है)	undefined
Meaning	Intentional absence	Unintentional absence
Assign कौन करता है	Programmer explicitly	JavaScript automatically
Examples	let x = null;	let x; or function(param)

// undefined
let a;  // declared पर not assigned
console.log(a); // undefined

function test(param) {
    console.log(param); // undefined अगर pass न हो
}
test();

// null
let b = null;  // explicitly assigned
console.log(b); // null

console.log(null == undefined);   // true
console.log(null === undefined);  // false
console.log(typeof null);         // 'object' (bug!)
console.log(typeof undefined);    // 'undefined'

इंटरव्यू टिप: समझाएं null intentional है (developer sets करता है) जबकि undefined unintentional है (JavaScript sets करता है)। typeof null === 'object' का ज़िक्र करें।

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