As a follow-up to my "New Application Journey" article, I wanted to focus on how FormBuilder in Angular improves the process of form-based aspects of your application, while introducing some reactive programming concepts along the way.

Recap

As a TL;DR (too long, didn't read) to the original article, I wasn't happy with the application my mother-in-law was using for her very small business in the southeast section of the United States. So, I used her business needs to create a new application from scratch using Angular, MySQL, and the AWS environment. Since the application had a few forms to introduce, I was dreading the dated process I have been using — going all the way back to my introduction to AngularJS back in 2013.

Then, I noticed there was a FormBuilder in Angular, which used reactive programming concepts. This added a new layer of excitement for my new application journey.

What Is Reactive Programming?

According to Wikipedia, reactive programming is a declarative programming paradigm concerned with data streams and the propagation of change.

The Wikipedia page provides an example that I always recall when explaining reactive programming to new members of a current project. Typically, when using imperative programming the following line of code might be executed in a method or function:

 a = b + c 

Prior to reactive programming, the variable a would be set to the sum of the current values of b and c at the time the line of code was executed. If later in the method, b  or c changed, the value of a would remain the same.

Reactive programming would consider each variable as a stream, with the concept that a will always equal the sum of b and c. Thus, if b or c changed, the value of a would automatically change.

Angular FormBuilder

When building forms in the current version of Angular there are two options. The first is the typical template-based approach which relies on less explicit, unstructured data model, directives, and asynchronous predictability. The other is a reactive approach which relies on a more explicit, structured data model, functions, and synchronous predictability.

Since I had used the template approach for quite some time, I was excited to try the FormBuilder in a reactive mode. 

A Simple Example

The following screenshot was shared in my original "New Application Journey" article:

This is a simple form, which has required fields for Property Name, Sales Price, and Commission amount. Since this screen shot was created, we removed the titleDate and only now have a closingDate. The closingDate field is also required, but have a default value that can only be changed and not removed.

I needed to setup the FormBuilder object in Angular.

The constructor of my class included an inject of the FormBuilder class, as shown below:

constructor(private formBuilder: FormBuilder, ...) {
this.createForm();
}

When the constructor fires, the createForm() method is called, which establishes the propertyForm object:

private createForm(): void {
    this.propertyForm = this.formBuilder.group({
      property: this.formBuilder.group({
        propertyName: ['', Validators.required],
        closingDate: '',
        agentSales: '',
        lastName:  '',
        agentInitials: '',
        salesPrice: ['', Validators.required],
        county: '',
        exemptAmount: '',
        baseTax: '',
        surtax: '',
        totalSalesTax: '',
        commission: ['', Validators.required],
        profit: '',
        totalAgentAmount: '',
        referralName: '',
        referralAmount: ''
      }),
      closingDate: ['', Validators.required],
    });
  }

My propertyForm includes a property object, which matches my DTO and a closingDate object — which is used for the NgbDateStruct implementation for the Closing Date field.

To initialize a new property on the form, I called a private method to establish the default values:

private createNewProperty(): void {
    const today = new Date();

    this.property = new Property();
    this.property.propertyName = null;
    this.property.closingDate = today.getTime();
    this.property.salesPrice = null;
    this.property.commission = null;

    this.closingDate = {
      year: today.getFullYear(),
      month: today.getMonth() + 1,
      day: today.getDate()
    };

    this.propertyForm.setValue({property: this.property, closingDate: this.closingDate});

When I need to push values into the FormBuilder object, I use the setValue() or patchValue() methods. When I want to retrieve values from the FormBuilder object, I use the value attributes on the this.propertyForm object.

The biggest challenge I ran into with this form was getting the this.closingDate values into thethis.property.closingDate attribute. The former is a JSON object with attributes for year, month, and day, while the latter is a Date() object.

Looking Ahead

This article is a continuation of a multi-part series that I am putting together regarding my new application journey to providing a better application experience for my mother-in-law. Below, is a list of the current and planned articles, if you are interested in reading more:

• New Application Journey

• Okta, a nice solution - even for small apps

• FormBuilder in Angular 6 (this article)

• The Challenge of the Commission Report

• Making the County List Dynamic

• New Version of the Commission Report

• What I Learned After Initial Deployment

Have a really great day!