Lodash _.findLastIndex() Function

Lodash is a JavaScript library that works on the top of underscore.js. Lodash helps in working with arrays, strings, objects, numbers, etc.
The _.findLastIndex() function is used to find the element from the right of the array. Therefore giving the index of the last occurrence of the element in the array.

Syntax:

findLastIndex(array, [predicate=_.identity], fromIndex);

Parameter:

  • array: It is the original array.
  • predicate: It is the function that iterates over each element.
  • fromIndex: It is the index after which the searching starts. If from Index is not given then by default it is n-1 where n is the length of the array.

Return Value: It returns the index of the element if found else -1 is returned.

Note: Install lodash module by using command npm install lodash before using the code given below. 



Example 1: 

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// Requiring the lodash library
const _ = require("lodash");
  
// Original array
let array1 = [4, 2, 3, 1, 4, 2]
  
// Using lodash.findLastIndex
let index = _.findLastIndex(array1, (e) => {
    return e == 2;
});
  
// Original Array
console.log("original Array: ", array1)
  
// Printing the index
console.log("index: ", index)

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Output: 

Example 2: When an element is present in the array but the output is -1 because it is present after the from the index. Here fromIndex is 2.

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// Requiring the lodash library
const _ = require("lodash");
  
// Original array
let array1 = [4, 2, 3, 1, 4, 2]
  
// Using lodash.findLastIndex
let index = _.findLastIndex(array1, (e) => {
    return e == 1;
}, 2);
  
// Original Array
console.log("original Array: ", array1)
  
// Printing the index
console.log("index: ", index)

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Output: 

Example 3: When an array of objects is given.

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// Requiring the lodash library
const _ = require("lodash");
  
// Original array
let array1 = [
    { "a": 1, "b": 2 }, 
    { "b": 4 }, 
    { "a": 1 }
]
  
// Using lodash.findLastIndex
let index = lodash.findLastIndex(array1, (e) => {
    return e.b == 2;
}, 2);
  
// Original Array
console.log("original Array: ", array1)
  
// Printing the index
console.log("index: ", index)

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Output: 

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