Form Validation Using a Boolean Flag in Angular 8

Описание: Explore how to implement effective form validation in Angular 8 using boolean flags and manage the validity of dynamic fields seamlessly.
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Form Validation Using a Boolean Flag in Angular 8

Form validation is a critical aspect of developing user-friendly applications, and Angular 8 provides various tools to ensure that your forms behave correctly. In this guide, we will address a common problem faced when handling dynamic forms in Angular and offer a streamlined solution to validate form fields based on user input.

The Problem

Imagine you have a dynamic form where users can input values that must adhere to specific rules. For instance, in this case, we want users to enter values less than 10. If any input exceeds this threshold, we want to display an error message only for that specific input field. However, in the initial implementation, an error message was shown for all fields if any single input was invalid, which is clearly not the desired behavior.

Sample HTML Structure

Here’s an example of the HTML and TypeScript code that we are working with:

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TypeScript Function

The existing TypeScript function checks all values in a loop but does not differentiate which field is invalid:

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

The challenge here is to only trigger the error message for the specific field that exceeds 10.

The Solution

To fix this issue, we will modify our implementation. By creating a method that checks the validity of specific fields, we can streamline our validation process. Here are the steps to achieve this:

Step 1: Update the HTML Code

Firstly, update your HTML code to call a new method that returns the validation state for each field individually:

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

Step 2: Create the Validation Method

Add the isInvalid method in your TypeScript file to check if the specific field is greater than 10:

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

Step 3: Modify the Limit User Function

While we are at it, let’s refine the existing limitUser function to handle default values effectively and ensure it’s checking properly:

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

Step 4: Manage the Overall Form Validity

To disable the submit button when any field is invalid, create a computed property to check the overall state of the form:

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

And modify your button to disable it based on this property:

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

Conclusion

By following these steps, you can ensure that your Angular 8 forms provide interactive feedback specific to each field. This not only improves the user experience but also keeps your validation logic clean and maintainable. Remember, the key takeaway is to have distinct validation checks for dynamic fields, avoiding blanket error messages that can confuse users. Your forms can be smarter and your validation can be clearer, reinforcing a better interaction overall.