Interview question

What is the difference between find(), findIndex(), some(), and every()? find(), findIndex(), some(), और every() में क्या अंतर है?

Answer

Method	Returns	Stops early?
find()	The first matching element, or undefined	Yes, on first match
findIndex()	Index of first match, or -1	Yes, on first match
some()	true if ANY element matches	Yes, on first true
every()	true only if ALL elements match	Yes, on first false

const users = [
    { id: 1, name: 'John', active: true },
    { id: 2, name: 'Jane', active: false },
    { id: 3, name: 'Bob', active: true }
];

// find - returns the actual element
const inactiveUser = users.find(u => !u.active);
console.log(inactiveUser); // { id: 2, name: 'Jane', active: false }

const notFound = users.find(u => u.id === 99);
console.log(notFound); // undefined

// findIndex - returns the position
const index = users.findIndex(u => u.name === 'Bob');
console.log(index); // 2
console.log(users.findIndex(u => u.name === 'Nobody')); // -1

// some - true if AT LEAST ONE matches (like logical OR across the array)
const hasInactive = users.some(u => !u.active);
console.log(hasInactive); // true

// every - true only if ALL match (like logical AND across the array)
const allActive = users.every(u => u.active);
console.log(allActive); // false - Jane is inactive

// Practical use: validating a form's fields
const fields = [{ valid: true }, { valid: true }, { valid: false }];
const formIsValid = fields.every(f => f.valid);
console.log(formIsValid); // false

// Practical use: checking permission - does user have ANY admin role?
const roles = ['editor', 'viewer'];
const isAdmin = roles.some(role => role === 'admin');
console.log(isAdmin); // false

// Performance note: all four short-circuit, stopping as soon as the answer is known
// - useful for large arrays where you don't need to process every element

Method	Return	जल्दी रुकता है?
find()	पहला matching element, या undefined	हाँ, पहले match पर
findIndex()	पहले match का index, या -1	हाँ
some()	true अगर कोई एक match करे	हाँ
every()	true सिर्फ अगर सभी match करें	हाँ

const users = [
    { id: 1, name: 'John', active: true },
    { id: 2, name: 'Jane', active: false },
    { id: 3, name: 'Bob', active: true }
];

// find - actual element return करता है
const inactiveUser = users.find(u => !u.active);
console.log(inactiveUser); // { id: 2, ... }

// findIndex - position return करता है
const index = users.findIndex(u => u.name === 'Bob');
console.log(index); // 2

// some - कम से कम एक match हो तो true
const hasInactive = users.some(u => !u.active);
console.log(hasInactive); // true

// every - सभी match हों तभी true
const allActive = users.every(u => u.active);
console.log(allActive); // false

// Form validation
const fields = [{ valid: true }, { valid: true }, { valid: false }];
const formIsValid = fields.every(f => f.valid);
console.log(formIsValid); // false

// Permission check
const roles = ['editor', 'viewer'];
const isAdmin = roles.some(role => role === 'admin');
console.log(isAdmin); // false

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