An Introduction to SetValue & PatchValue in Angular

The Angular framework is an extremely popular and powerful web development platform that allows developers to create dynamic, responsive web applications with ease. One of its key features is the ability to work with reactive forms, which enable developers to create complex forms that can be used to collect user data, among other things. SetValue and PatchValue are two important methods in Angular that form the backbone of reactive form development, allowing developers to manipulate form data with ease.

What is SetValue?

SetValue is a method in Angular that allows developers to set the value of a specific form control, group or array. This method is used to set the value of a form control or group to a static value, or to an object or an array of objects.

Example:

Suppose we have a form with three controls, namely name, email and message. We can use the SetValue method to set the value of each control as follows:

“`typescript
this.contactForm.setValue({
name: ‘John Doe’,
email: ‘johndoe@gmail.com’,
message: ‘Hello, world!’
});
“`

This code sets the name control to ‘John Doe’, the email control to ‘johndoe@gmail.com’ and the message control to ‘Hello, world!’.

What is PatchValue?

PatchValue is another method in Angular that allows developers to update the value of a specific form control, group or array. This method is used to apply changes to the existing value of a form control or group.

Example:

Suppose we have a form with three controls, namely name, email and message. We can use the PatchValue method to update the value of the name control as follows:

“`typescript
this.contactForm.patchValue({
name: ‘Jane Doe’
});
“`

This code updates the name control to ‘Jane Doe’, while leaving the values of the other controls unchanged.

What is the difference between SetValue and PatchValue?

The main difference between SetValue and PatchValue is that SetValue overwrites the entire value of a form control or group with a new value, whereas PatchValue updates specific properties of an existing value.

Use SetValue when you have a complete value for a form control or group, and you want to replace the existing value with the new value. Use PatchValue when you only need to update some properties of an existing value.

When should I use SetValue or PatchValue?

You should use SetValue when you have a complete value for a form control or group, and you want to replace the existing value with the new value.

On the other hand, you should use PatchValue when you only need to update some properties of an existing value.

What happens if I try to use SetValue or PatchValue on a non-existent form control or group?

If you try to use SetValue or PatchValue on a non-existent form control or group, Angular will throw an error.

What happens if I try to use SetValue or PatchValue on a disabled form control or group?

If you try to use SetValue or PatchValue on a disabled form control or group, Angular will throw an error.

What is a possible use case for SetValue or PatchValue?

SetValue and PatchValue are useful for a range of scenarios, such as:

  • Setting the initial values of a form

  • Updating the values of a form based on user input or other events

  • Resetting the values of a form to their default values

  • Populating a form with data from an external source, such as an API

In conclusion

SetValue and PatchValue are two vital methods in Angular that are used extensively in reactive form development. Understanding the difference between the two methods and when to use them is crucial for creating robust, dynamic web applications that provide an enhanced user experience.

FAQs

Q. Can SetValue or PatchValue be used for both synchronous and asynchronous operations?

A. Yes, SetValue and PatchValue can be used for both synchronous and asynchronous operations.

Q. Can SetValue and PatchValue be used on arrays?

A. Yes, SetValue and PatchValue can be used on arrays.

Q. Are there any performance implications of using SetValue or PatchValue on large forms?

A. Using SetValue or PatchValue on large forms can potentially impact performance, so it is important to use these methods judiciously.

Q. When should I use SetValue over PatchValue?

A. You should use SetValue when you have a complete value for a form control or group, and you want to replace the existing value with the new value. Use PatchValue when you only need to update some properties of an existing value.

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