Syntax, Parameter, and Return Value
Syntax:
_.findIndex(array, [predicate=_.identity], [fromIndex=0])
Parameters:
-
array (Array): The array to inspect.
-
predicate (Function): The function invoked per iteration.
- fromIndex (optional, number): The index to search from, default is 0.
Return Value:
The index of the first element predicate returns truthy for, else -1.
Examples
Basic Usage:
Finding the index of the first positive number.
JavaScript
let numbers = [-3, -2, -1, 0, 1, 2];
let index = _.findIndex(numbers, (n) => n > 0);
console.log(index);
You can also try this code with Online Javascript Compiler
Output:
4
Object Array:
Finding the index of an object where a property matches a value.
JavaScript
let users = [
{ 'user': 'barney', 'active': false },
{ 'user': 'fred', 'active': false },
{ 'user': 'pebbles', 'active': true }
];
let index = _.findIndex(users, { 'user': 'fred', 'active': false });
console.log(index);
You can also try this code with Online Javascript Compiler
Output:
1
Using a Custom Predicate Function:
Using a custom function to find the index of an element.
JavaScript
let numbers = [1, 2, 3, 4, 5];
let index = _.findIndex(numbers, (n) => n % 2 === 0);
console.log(index);
You can also try this code with Online Javascript Compiler
Output:
1
Specifying Start Index:
Starting the search from a specific index.
JavaScript
let numbers = [1, 2, 3, 4, 5];
let index = _.findIndex(numbers, (n) => n > 3, 2);
console.log(index);
You can also try this code with Online Javascript Compiler
Output:
3
Frequently Asked Questions
What happens if no element satisfies the predicate?
If no element satisfies the predicate, _.findIndex() returns -1, indicating no match was found.
Can _.findIndex() handle nested objects or arrays?
Yes, it can handle nested structures, provided the predicate function is designed to navigate and evaluate them appropriately.
How is _.findIndex() different from Array.prototype.findIndex()?
While both perform similar tasks, _.findIndex() offers more flexibility with predicates and consistent behavior across different JavaScript environments.
Conclusion
Lodash's _.findIndex() method is a robust and convenient tool for locating the index of the first element in an array that satisfies a specific condition. It simplifies the task of searching through arrays, particularly those with complex structures or large data sets. With its flexible predicate functions and easy-to-understand syntax, _.findIndex() enhances the efficiency of JavaScript coding, especially in scenarios involving data searching, manipulation, and UI-related operations.
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