Syntax, Parameter and Return Value
Syntax:
_.findLastKey(object, [predicate=_.identity])
Parameters:
-
object (Object): The object to inspect.
- [predicate=_.identity] (Function): The function invoked per iteration.
Return Value:
(string|undefined) - Returns the key of the matched element, else undefined.
Examples
Finding the Last Key Based on a Condition:
JavaScript
var _ = require('lodash');
var users = {
'barney': { 'age': 36, 'active': false },
'fred': { 'age': 40, 'active': false },
'pebbles': { 'age': 1, 'active': true }
};
var key = _.findLastKey(users, function(o) { return o.active; });
console.log(key);
You can also try this code with Online Javascript Compiler
Output:
'pebbles'
Demonstrates finding the key of the last user who is active.
Using a Shorthand with Property Value:
JavaScript
var key = _.findLastKey(users, { 'age': 36, 'active': false });
console.log(key);
You can also try this code with Online Javascript Compiler
Output:
'barney'
Shows how to use object literal shorthand to find the last matching key.
Using a Property Name Shorthand:
JavaScript
var key = _.findLastKey(users, 'active');
console.log(key);
You can also try this code with Online Javascript Compiler
Output:
'pebbles'
An example of using property name shorthand to find the key of the last active user.
Matching Against a Property Value:
JavaScript
var key = _.findLastKey(users, ['active', false]);
console.log(key);
You can also try this code with Online Javascript Compiler
Output:
'fred'
Demonstrates finding the key of the last user where the 'active' property is false.
Frequently Asked Questions
How does _.findLastKey() differ from _.findKey()?
_.findKey() returns the key of the first element that satisfies the predicate, while _.findLastKey() returns the key of the last element that satisfies the predicate.
What happens if no element satisfies the predicate?
If no element satisfies the predicate, _.findLastKey() returns undefined.
Can _.findLastKey() be used with arrays?
While _.findLastKey() is primarily designed for objects, it can be used with arrays. However, since array indices are less informative than object keys, array-specific methods are usually more suitable for arrays.
Conclusion
Lodash's _.findLastKey() method offers an effective way to search for the last key in an object that meets a specific condition. It is particularly useful for ordered objects or when the most recent (last) match based on certain criteria is required.
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