Understanding Why Your JavaScript Function Returns Array(0) in React

Learn how to fix your JavaScript function that returns an empty array when generating days of a month in React.
---

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: I'm learning javascript and react and I don't understand why the function returns Array(0)

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
Why Does My JavaScript Function Return Array(0) in React?

If you are learning JavaScript and React, you may wonder why your function unexpectedly returns Array(0) instead of the dates you expect. This is a common issue faced by beginner programmers, especially when dealing with dates and time. Let's dig deeper into this problem and understand how to resolve it effectively!

The Problem

You are trying to create a monthly schedule that dynamically adjusts the displayed dates based on the month and year. However, the function you've written returns an empty array. Here’s the relevant portion of your code:

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

The major issue lies within the loop where you try to populate the jours array with dates for the current month. Let's explore the reasons behind the unexpected output.

Understanding the Code Structure

The function genererJoursDuMois aims to generate all the dates of the current month based on the state moisActuel. Here is a quick overview of what the function is doing:

Initialises an empty array: This will hold the days of the month.

Creates a starting date: It specifies the first day of the month using the moisActuel state.

Determines the last day of the month: This is where the function fails due to an improper comparison.

The Error Explained

The crux of the issue is found in the loop's condition of your original code:

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

Here, jour is being compared to dernierJourDuMois, which is an integer representing the last day of the month (e.g., 30 or 31). This causes an error because you are attempting to compare a Date object to a number, leading to a false condition each time, thus returning an empty array.

The Solution

To fix this, you should modify the dernierJourDuMois to be a Date object rather than just an integer. Here’s how to correct your code:

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

Key Changes Made:

Stored dernierJourDuMois as a Date Object: This allows for a proper comparison in the loop.

Checked Dates with Date Objects: Comparing jour (Date object) to dernierJourDuMois (Date object) ensures the loop runs as expected.

Conclusion

By modifying your comparison and ensuring that both sides of the condition are of the same type (Date objects), your function should now correctly populate jours with the days of the month. Such issues are common but manageable with clear attention to how comparisons work in JavaScript.

Now that you've understood the problem and implemented a solution, you can confidently move forward in your JavaScript and React journey. Happy coding!