Selecting the last element in a JavaScript array

javascript

array-methods

performance-optimization

javascript-features

byAnton Shumikhin·Dec 27, 2024

Need the last item in an array arr? Here's your one-liner:

let lastElement = arr[arr.length - 1]; // No more lonely nights (or elements)!

The arr.length - 1 returns the last index in your array, promptly fetching the tail element.

Methods to select array tail element

Often, we need a more overarching understanding of the process, to select the right method depending on our needs. Let's deep-dive into best practices.

Opt for non-destructive

arr.slice(-1)[0] saves the day by providing the last element and importantly, preserving the array. Paired with efficiency, these merits make it a champion in real-time applications:

let safeLastElement = arr.slice(-1)[0]; // smart move, isn't it?

ES6 magic: Destructuring

ES6 allows for a slightly more expressive syntax with destructuring:

let [...rest, last] = arr;

Yet, don't get over excited! This method can be sneaky with large arrays; it makes a copy, which might hit performance.

Performance is key

Especially in real-time applications (e.g., updating a Google Map marker), optimized code is an absolute must. Don't create a new marker; update the pre-existing marker's position:

mapMarker.setPosition({lat: coords.latitude, lng: coords.longitude}); // I'm not lost, I'm just exploring

This tactics treads lightly on performance while maintaining real-time responsiveness.

Create shortcuts for repetitive tasks

If fetching the last element has become your daily chore, consider creating a shortcut. Extending the Array prototype to add a last() method can help, but tread carefully:

if (!Array.prototype.last){
    Array.prototype.last = function(){
        return this[this.length - 1];
    };
}

Now, arrayTrain.last() elegantly fetches the last car in your array. But beware: modifying native prototypes can lead to surprise plot twists in large codebases or libraries!