Javascript Array - findLastIndex() Method

Tutorialsrack 25/09/2022 Jquery Javascript

In this article, you will learn about the javascript Array built-in method Array.prototype.findLastIndex().  How does this method work in javascript? 

Array.prototype.findLastIndex()

This Array.prototype.findLastIndex() method returns the index of the last element from the provided array which passes the test that is implemented by the callback() function. If no elements pass the test, it returns -1.

array.findLastIndex(callback(element [, index [, array]]) [,thisParameter]);

This method takes 2 parameters as given below:

• callback: This parameter holds the function to be called for each element of the array. This function takes the mentioned parameters as below:
• element: This parameter holds the current element of the array.
• Index(Optional): This parameter holds the index of the current element within the array.
• array(Optional): This parameter holds the reference to the original array.
• thisParameter(Optional): This parameter holds the context to be passed as this to be used while executing the callback function.

The findLastIndex() method does not execute the callback function for empty elements. And it does not change the original array.

Here are some examples of Array.prototype.findLastIndex() method:

//find the last element in an array which is greater than 30
console.log([12, 5, 8, 130, 44].findLastIndex(x => x > 30));
// output => 4

//find the last element in an array that is greater than 130
console.log([12, 5, 8, 130, 44].findLastIndex(x => x > 130));
// output => -1


let cities = [
    {name: 'Los Angeles', population: 3792621},
    {name: 'New York', population: 8175133},
    {name: 'Chicago', population: 2695598},
    {name: 'Houston', population: 2099451},
    {name: 'Philadelphia', population: 1526006}
];

//find the last element of the city where the population is greater than 5000000
let metroCities = cities.findLastIndex(city => city.population > 5000000);
console.log(metroCities);
//output => 1

I hope this article will help you to understand the javascript Array built-in method Array.prototype.findLastIndex(). 

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