findKey

Finds the key of the first element in the object that satisfies the provided testing function.

Signature

function findKey<T extends Record<any, any>>(
  obj: T,
  predicate: (value: T[keyof T], key: keyof T, obj: T) => boolean
): keyof T | undefined;

Parameters

• obj (T extends Record<any, any>): The object to search.
• predicate ((value: T[keyof T], key: keyof T, obj: T) => boolean): The function to execute on each value in the object.

Returns

(keyof T | undefined): The key of the first element in the object that satisfies the provided testing function, or undefined if no element passes the test.

Examples

const users = {
  pebbles: { age: 24, active: true },
  barney: { age: 36, active: true },
  fred: { age: 40, active: false },
};

findKey(users, o => o.age < 40); // 'pebbles'
findKey(users, o => o.age > 50); // undefined

Compatibility with Lodash

Import findKey from es-toolkit/compat for full compatibility with lodash.

You can specify the condition for finding keys in several ways:

• Predicate function: You can provide a predicate function that will be applied to each value in the object. The function should return true for elements that match the criteria. The search continues until the predicate returns true for the first time.
• Partial object: You can also provide a partial object, and the function will return the key of the first element in the object that matches the properties of the provided object.
• Property-value pair: Alternatively, you can specify a property-value pair, where the function will return the key of the first element that has the specified property matching the given value.
• Property name: Lastly, you can provide a property name, and the function will return the key of the first element where the specified property has a truthy value.

Signature

export function findKey<T extends Record<any, any>>(
  obj: T,
  conditionToFind: (value: T[keyof T], key: keyof T, obj: T) => boolean
): keyof T | undefined;
export function findKey<T extends Record<any, any>>(obj: T, objectToFind: Partial<T[keyof T]>): keyof T | undefined;
export function findKey<T extends Record<any, any>>(
  obj: T,
  propertyToFind: [keyof T[keyof T], any]
): keyof T | undefined;
export function findKey<T extends Record<any, any>>(obj: T, propertyToFind: keyof T[keyof T]): keyof T | undefined;

Examples

const users = { barney: { age: 36 }, fred: { age: 40 } };

findKey(users, o => o.age < 40);
// => 'barney'
findKey(users, { age: 36 });
// => 'barney'
findKey(users, ['age', 36]);
// => 'barney'

const languages = { javascript: { active: false }, typescript: { active: true } };
findKey(users, 'active');
// => 'typescript'