Lodash _.findLast() Method

Syntax, Parameter and Return Value

Syntax: 

_.findLast(collection, [predicate=_.identity], [fromIndex=collection.length-1])

Parameters:

• collection (Array|Object): The collection to inspect.
   
• [predicate=_.identity] (Function): The function invoked per iteration.
   
• [fromIndex=collection.length-1] (number): The index to start the search from, backward.

Return Value: 

Returns the matched element, else undefined.

Examples

Finding Last Matching Number:

• JavaScript

JavaScript

var _ = require('lodash');

var numbers = [1, 2, 3, 4, 5, 3, 6];

var lastThree = _.findLast(numbers, n => n === 3);

console.log(lastThree); 

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Output: 

3

This example illustrates finding the last occurrence of the number 3 in an array.

Searching for the Last Object with a Specific Property:

• JavaScript

JavaScript

var users = [{ 'user': 'barney', 'active': true },

             { 'user': 'fred',   'active': false },

             { 'user': 'pebbles', 'active': true }];

var lastActiveUser = _.findLast(users, { 'active': true });

console.log(lastActiveUser); 

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Output: 

{ 'user': 'pebbles', 'active': true }

Demonstrates locating the last object in an array that has a specified property value.

Finding the Last Element in an Object:

• JavaScript

JavaScript

var object = { 'a': 1, 'b': 2, 'c': 3, 'd': 2 };

var lastTwo = _.findLast(object, v => v === 2);

console.log(lastTwo); 

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Output: 

2

Shows how to find the last occurrence of a value in an object.

Using a Property Name Shorthand:

• JavaScript

JavaScript

var products = [{ 'name': 'apple', 'inStock': false }, 

                { 'name': 'banana', 'inStock': true },

                { 'name': 'pear', 'inStock': true }];

var lastInStock = _.findLast(products, 'inStock');

console.log(lastInStock); 

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Output:

{ 'name': 'pear', 'inStock': true }

Utilizes Lodash's shorthand syntax for simpler and more concise code.

Frequently Asked Questions 

How does _.findLast() compare with _.find()?

While _.find() returns the first element that meets the criteria, _.findLast() searches from the end of the collection, returning the last matching element.

Can _.findLast() be used with a negative fromIndex?

Yes, a negative fromIndex starts the search from the end of the collection, moving backwards.

Is _.findLast() suitable for searching large collections?

It is suitable, but the efficiency depends on the collection size and predicate complexity; it may be less efficient for very large collections.

Conclusion

Lodash's _.findLast() method is a highly useful tool for situations where the last occurrence of a matching element in a collection is of interest. It extends the functionality of searching in arrays and objects, offering a more targeted and efficient approach, especially in scenarios where the most recent data is most relevant.

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