For AI agents: the complete documentation index is available at /llms.txt, the full documentation bundle is available at /llms-full.txt, and this page is available as Markdown at /reference/object/findKey.md.
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    findKey es-toolkit

    Finds the key of the first element that satisfies the given condition.

    const key = findKey(obj, predicate);

    Usage

    findKey(obj, predicate)

    Use findKey when you want to find the key of the first element in an object that satisfies a specific condition. It returns the key for the first value where the condition function returns true.

    import { findKey } from 'es-toolkit/object';

// Find the first user under 30 years old
const users = {
  alice: { age: 25, active: true },
  bob: { age: 30, active: false },
  charlie: { age: 35, active: true },
};

const youngUserKey = findKey(users, user => user.age < 30);
console.log(youngUserKey); // 'alice'

// Find an inactive user
const inactiveUserKey = findKey(users, user => !user.active);
console.log(inactiveUserKey); // 'bob'

// When no element satisfies the condition
const seniorUserKey = findKey(users, user => user.age > 50);
console.log(seniorUserKey); // undefined

    The condition function receives the current value, key, and the entire object.

    const data = {
  item1: { priority: 'high', status: 'pending' },
  item2: { priority: 'low', status: 'done' },
  item3: { priority: 'high', status: 'done' },
};

// Search considering both key name and value
const result = findKey(data, (value, key, obj) => {
  return key.includes('2') && value.status === 'done';
});
console.log(result); // 'item2'

    Can also be used with complex object structures.

    const products = {
  laptop: {
    specs: { ram: 16, cpu: 'Intel i7' },
    price: 1200,
    available: true,
  },
  phone: {
    specs: { ram: 8, cpu: 'Snapdragon' },
    price: 800,
    available: false,
  },
  tablet: {
    specs: { ram: 12, cpu: 'Apple M1' },
    price: 1000,
    available: true,
  },
};

const affordableKey = findKey(products, product => product.price < 1000 && product.available);
console.log(affordableKey); // undefined (no product satisfies the condition)

const highRamKey = findKey(products, product => product.specs.ram >= 12);
console.log(highRamKey); // 'laptop'

    Parameters

    objT extends Record<any, any>required

    The object to search.

    predicate(value: T[keyof T], key: keyof T, obj: T) => booleanrequired

    A condition function to execute for each element. Finds the key of the first element that returns true.

    Returns

    The key of the first element that satisfies the condition. Returns undefined if no element satisfies the condition.

    keyof T | undefined
    Source: es-toolkit

    Re-exported verbatim from es-toolkit. Implementation, edge cases, and performance behavior are owned upstream. This page mirrors the documentation at the pinned version; the linked source is authoritative.