Скачать или смотреть How to Create a Method for a Function in JavaScript to Get Last Item from an Array

Discover how to effectively create a method for a function in JavaScript that retrieves the `last` item from an array. Learn step-by-step instructions and see practical code snippets to enhance your understanding!
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This video is based on the question https://stackoverflow.com/q/63590460/ asked by the user 'Mathew' ( https://stackoverflow.com/u/13720421/ ) and on the answer https://stackoverflow.com/a/63590517/ provided by the user 'CertainPerformance' ( https://stackoverflow.com/u/9515207/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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How to Create a Method for a Function in JavaScript to Get Last Item from an Array

In the world of JavaScript programming, creating reusable functions is crucial for clean and efficient code. Today, we'll tackle a common challenge: how to create a method that allows you to get the last item from an array. We will delve into a specific use case where you want to extend your selector function, $$, to include this feature.

Understanding the Problem

You have a selector function that retrieves elements from the DOM. The goal is to enhance this function to enable it to get the last item of the resulting array of elements. The initial implementation attempts to add a method directly to the function's prototype, but it encounters an error. Let's clarify what went wrong and how to solve it.

Initial Approach

Your initial function was defined as follows:

[[See Video to Reveal this Text or Code Snippet]]

You attempted to add a method to the prototype like so:

[[See Video to Reveal this Text or Code Snippet]]

However, this throws an error: Uncaught TypeError: Cannot set property 'getLastItem' of undefined. The reason for this error is that $$ is a function and not an object with a prototype that can be easily extended in that manner.

The Solution: Creating a Class Method

Instead of adding a method to a function prototype, the best approach is to encapsulate the functionality within a class. This not only redefines how we structure our code, but it also allows us to create a method that directly interacts with our selected elements.

Using a Class to Define Our Functionality

Here's how we can implement a Dollar class that introduces a getLastItem method:

[[See Video to Reveal this Text or Code Snippet]]

Breakdown of the Class Implementation

Class Declaration: We define a class named Dollar which will encapsulate our functionality.

Constructor: The constructor takes a selector and an optional parent parameter, allowing you to search for elements within a specific context (defaulting to document).

Storing Elements: We use the spread operator to convert the NodeList returned by querySelectorAll into an array stored in this.elements.

Method Definition: The getLastItem() method uses slice() to retrieve the last element from this.elements.

Creating an Instance: The function $$ creates an instance of Dollar which closely replicates the original functionality while providing additional features.

Accessing Elements

If you'd like to access specific elements directly without always using the getLastItem method, you can extend the class further:

[[See Video to Reveal this Text or Code Snippet]]

What This Approach Achieves

Clean Code: By using a class, your code is modular and easier to read.

Extensibility: You can easily add more methods to the Dollar class as your needs grow.

Direct Access: This structure allows you to access the elements array directly as well as through methods.

Conclusion

Understanding how to create methods for functions in JavaScript opens up new possibilities for your coding. By encapsulating functionality in classes, we promote cleaner, more maintainable code. The class-based approach also helps resolve issues related to the prototype and improves how methods can interact with stored data.

Next time you're building reusable functions, consider leveraging the power of classes in JavaScript to enhance your overall code quality.