Скачать или смотреть Resolving the TypeError in VueJS: A Guide to Highlighting Active Menu Tabs

Learn how to fix the `TypeError: Cannot read property 'className' of undefined` in your VueJS application while highlighting active menu tabs with this step-by-step solution.
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This video is based on the question https://stackoverflow.com/q/62980776/ asked by the user 'NuzzeSicK' ( https://stackoverflow.com/u/9196570/ ) and on the answer https://stackoverflow.com/a/62981524/ provided by the user 'AlekseyHoffman' ( https://stackoverflow.com/u/12125881/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Resolving the TypeError in VueJS: A Guide to Highlighting Active Menu Tabs

In web development, especially when using frameworks like VueJS, errors can often disrupt the flow of creating a seamless user interface. One such error that developers might encounter is the TypeError: Cannot read property 'className' of undefined. This often occurs when attempting to manipulate the elements of your application directly when they may not be defined yet. In this guide, we will address this specific error and explore how to effectively highlight active menu tabs in your VueJS application.

Understanding the Problem

You might be trying to implement a menu system that allows users to see which tab they are currently viewing by highlighting it. In the code you provided, a menu with buttons is set up to display different countries while also attempting to manage the active state of the menu buttons. However, an attempt to access the className property of an undefined object leads to an error.

Here’s a brief summarization of the issue:

You are trying to highlight the current tab using JavaScript to add or remove classes.

When a tab is clicked, the openCity method is called.

Unfortunately, if the event handling is not done correctly, it can lead to the error mentioned above.

The Solution

Here are the steps to correct the issue and ensure that the current tab is highlighted properly in VueJS.

Step 1: Update the HTML Structure

First, let’s modify your HTML to leverage Vue’s capabilities fully. Instead of directly invoking JavaScript events, use Vue’s built-in event handling methods:

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

Explanation:

We use the v-for directive to loop through the cities and create buttons dynamically.

The @ click directive is Vue's way of registering click events and effectively allows us to pass the event and the city object into the openCity method while maintaining reactive behavior.

Step 2: Modify the JavaScript Logic

In your Vue component’s script block, we will modify the openCity method to simply update the selected city instead of manipulating DOM elements directly:

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

Explanation:

The openCity method is simplified to only set the selectedCity, benefiting from Vue's reactive data binding system to handle updates in the UI.

Step 3: CSS for Visibility Control

Next, we will define CSS classes to handle the visibility of the content effectively:

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

Explanation:

Two classes are defined: .hidden for elements that are not visible and .visible for the active content, allowing Vue to manage visibility based on the state.

Bonus Method: Using v-show

If you prefer less CSS management, you can also opt to use the v-show directive to show or hide elements based on the selected city:

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

Explanation:

The v-show directive will control the visibility based on the condition city.name === selectedCity, streamlining the handling further.

Conclusion

By making these adjustments to your VueJS application, you can resolve the TypeError related to undefined properties and ensure that the current tab highlights correctly. Using Vue's built-in reactive features leads to cleaner, more maintainable code and enhances the overall user experience. Happy coding!