Lodash _.findLastKey() Method

The Lodash _.findLastKey() Method is like the _.findKey() method except that it iterates over elements of a collection in the opposite order.

Syntax:

_.findLastKey( object, predicate_function)

Parameters: This method accepts two parameters as mentioned above and described below:

• object: This parameter holds the object to find in.
• predicate_function: Function that is invoked per iteration.

Return Value: This method returns the key of the matched element, else undefined.

Example 1:

Javascript

// Defining Lodash variable
const _ = require('lodash');

var users = {
  'Ram':  { 'mark': 100, 'status': "pass" },
  'Shyam': { 'mark': 90, 'status': "pass" },
  'Arnav': { 'mark': 50,  'status': "fail" }
};

console.log(_.findLastKey(users, function(s)
                { return s.mark > 80; }));

console.log(_.findLastKey(users,
        { 'mark': 100, 'status': "pass" }));

console.log(_.findLastKey(users,
        ['status', "fail"]));

console.log(_.findLastKey(users, 'status'));

Output:

Shyam
Ram
Arnav
Arnav

Example 2: returns undefined for values that don’t exist.

Javascript

// Defining Lodash variable
const _ = require('lodash');

var users = {
  'Ram':  { 'mark': 100, 'status': "pass" },
  'Shyam': { 'mark': 90, 'status': "pass" },
  'Arnav': { 'mark': 50,  'status': "fail" }
};

console.log(_.findLastKey(users, function(s)
        { return false; }));

console.log(_.findLastKey(users,
        { 'mark': 100, 'status': "fail" }));

console.log(_.findLastKey(users, ['status', ""]));

console.log(_.findLastKey(users, 'mark'));

Output:

undefined
undefined
undefined
Arnav

Note: This will not work in normal JavaScript because it requires the lodash library to be installed and can be installed using npm install lodash.