How to Restrict Input Values in Angular 2+ Using ngModelChange Effectively

Discover how to properly use `ngModelChange` in Angular 2+ to restrict number input values dynamically in real-time, ensuring a seamless user experience.
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Understanding Input Value Restrictions in Angular 2+

When working with forms in Angular, especially number input fields, it's common to face issues where users can enter values beyond predefined limits. One common requirement is to restrict a user from entering a number greater than a specific maximum—such as 100. In this guide, we will explore a question about using the Angular ngModelChange directive effectively to achieve this goal.

The Problem

Consider a scenario where you have a number input field and want to ensure that users can only input values up to a maximum of 100. The expected behavior is as follows:

If the user types "1", it is accepted.

Typing "1" again should also be fine.

However, if the user attempts to input "111", the value should automatically change to "100".

Unfortunately, issues arise when the user continues to type; the number doesn't update as expected, and they can continue to input additional digits without restriction.

Here is the relevant HTML and controller code to illustrate this problem:

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

Controller Code

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

This code updates the period variable but only does so successfully once. Further input does not update the input field as expected, indicating a problem with synchronization between the model and the view.

The Solution

To solve this issue, we can make a small adjustment to our onValueChange() method. The problem originates from updating the model value during the ngModelChange event, which causes the model to go out of sync with the input value. To address this, we will use setTimeout(). Here's how we can modify the function:

Step-by-Step Implementation

Change the onValueChange() Method:
We will utilize the setTimeout() function to ensure that our model updates asynchronously, allowing the view value to synchronize correctly.

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

Benefits of Using setTimeout():

Asynchronous Handling: It allows Angular to finish processing the current change detection cycle before applying the changes, which avoids breaking the synchronization.

Real-Time Update: This ensures that users get immediate feedback when they input numbers exceeding the maximum value.

Testing the Input Field:
After implementing this change, test the input field again. When the user exceeds 100, the number should automatically correct itself to 100, and they can no longer input values that exceed the limit.

Conclusion

By using setTimeout() inside your ngModelChange method, you can effectively manage input restrictions in Angular 2+ . This approach ensures a positive user experience by providing immediate feedback and maintaining synchronization between the model and the view. This small change can greatly enhance the usability of your forms in Angular applications.

Feel free to integrate this solution into your Angular projects to handle number restrictions efficiently!