Angular Async Validation

I recently posted about Angular 2 Form validation which didn’t cover asynchronous validation. This post does cover an async validation example …

I’ve put all the classes in the same file to make the example simpler to show and read. The example gives a textbox for the user to enter a product code and validates that the product code exists and puts a description at the side if it does.

Referencing an async validator in FormBuilder

The first key point is that you reference the async validator in the 3rd parameter in FormBuilder.group(). None async validators go in the 2nd parameter - I only have a async validator in my example.

constructor(builder: FormBuilder) {
    this.orderForm = builder.group({
        productCode: ["", , ProductValidator.productExists]
    });
}

Writing the async validator

The async validator needs to return a promise that in turn returns null if valid or something else if not valid. In this example, I am calling a ProductService class to check whether the product exists

class ProductValidator {
  static productExists(control: Control): { [key: string]: any } {
    return new Promise(resolve => {
      var productService = new ProductService();
      var product: Product;
      productService.getProduct(control.value).then(productFound => {
        if (productFound == null) {
          // need to return something if not ok
          resolve({ productExists: false });
        } else {
          // need to return null if ok
          resolve(null);
        }
      });
    });
  }
}

Here’s the full listing …

import { Component } from "angular2/core";
import {
  FORM_DIRECTIVES,
  Control,
  ControlGroup,
  FormBuilder,
  Validators
} from "angular2/common";

class Product {
  code: string;
  description: string;
}

class ProductService {
  public getProduct(productCode: string): Promise<Product> {
    return new Promise(resolve => {
      // simulate a call to a web api with a setTimeout()
      setTimeout(() => {
        // pretent these are our products in our database
        var products: Product[] = [
          { code: "P001", description: "Chai" },
          { code: "P002", description: "Tofu" },
          { code: "P003", description: "Pavlova" }
        ];
        // this is the product code we want to check exists
        var productCodeToCheck: string = productCode;
        // check if the product code exists
        var foundProduct: Product;
        products.forEach(function(product: Product) {
          if (productCodeToCheck === product.code) {
            foundProduct = product;
          }
        });
        resolve(foundProduct);
      }, 1000);
    });
  }
}
class ProductValidator {
  static productExists(control: Control): { [key: string]: any } {
    return new Promise(resolve => {
      var productService = new ProductService();
      var product: Product;
      productService.getProduct(control.value).then(productFound => {
        if (productFound == null) {
          // need to return something if not ok
          resolve({ productExists: false });
        } else {
          // need to return null if ok
          resolve(null);
        }
      });
    });
  }
}

@Component({
  selector: "my-app",
  template: `
    <form [ngFormModel]="orderForm">
      <div>
        <input
          #productCode
          type="text"
          placeholder="product code"
          ngControl="productCode"
          (keyup)="lookupDescription(productCode.value)"
        />
        <span>{{ productDescription }}</span>
      </div>
    </form>
  `,
  styles: [
    `
      .ng-invalid {
        border-left: 5px solid #a94442;
      }
    `
  ],
  directives: [FORM_DIRECTIVES]
})
export class AppComponent {
  public productDescription: string;
  orderForm: ControlGroup;
  constructor(builder: FormBuilder) {
    this.orderForm = builder.group({
      productCode: ["", , ProductValidator.productExists]
    });
  }
  lookupDescription(productCode) {
    // initialise the description before we lookup the description
    this.productDescription = "";
    // call a service to lookup the description
    var productService = new ProductService();
    var product: Product;
    productService.getProduct(productCode).then(productFound => {
      if (productFound) {
        // set the components productDescription which will automatically show in the UI
        this.productDescription = productFound.description;
      }
    });
  }
}

#angular #async validation

What is GEEK

Buddha Community

Christa Stehr

1598940617

Install Angular - Angular Environment Setup Process

Angular is a TypeScript based framework that works in synchronization with HTML, CSS, and JavaScript. To work with angular, domain knowledge of these 3 is required.

Installing Node.js and npm
Installing Angular CLI
Creating workspace
Deploying your First App

In this article, you will get to know about the Angular Environment setup process. After reading this article, you will be able to install, setup, create, and launch your own application in Angular. So let’s start!!!

Install Angular in Easy Steps

For Installing Angular on your Machine, there are 2 prerequisites:

Node.js
npm Package Manager

Node.js

First you need to have Node.js installed as Angular require current, active LTS or maintenance LTS version of Node.js

Download and Install Node.js version suitable for your machine’s operating system.

Npm Package Manager

Angular, Angular CLI and Angular applications are dependent on npm packages. By installing Node.js, you have automatically installed the npm Package manager which will be the base for installing angular in your system. To check the presence of npm client and Angular version check of npm client, run this command:

npm -v

Installing Angular CLI

Open Terminal/Command Prompt
To install Angular CLI, run the below command:

npm install -g @angular/cli

· After executing the command, Angular CLI will get installed within some time. You can check it using the following command

ng --version

Workspace Creation

Now as your Angular CLI is installed, you need to create a workspace to work upon your application. Methods for it are:

Using CLI
Using Visual Studio Code

1. Using CLI

To create a workspace:

Navigate to the desired directory where you want to create your workspace using cd command in the Terminal/Command prompt
Then in the directory write this command on your terminal and provide the name of the app which you want to create. In my case I have mentioned DataFlair:

Ng new YourAppName

After running this command, it will prompt you to select from various options about the CSS and other functionalities.

To leave everything to default, simply press the Enter or the Return key.

#angular tutorials #angular cli install #angular environment setup #angular version check #download angular #install angular #install angular cli

Roberta Ward

1593184320

Basics of Angular: Part-1

What is Angular? What it does? How we implement it in a project? So, here are some basics of angular to let you learn more about angular.

Angular is a Typescript-based open-source front-end web application platform. The Angular Team at Google and a community of individuals and corporations lead it. Angular lets you extend HTML’s syntax to express your apps’ components clearly. The angular resolves challenges while developing a single page and cross-platform applications. So, here the meaning of the single-page applications in angular is that the index.html file serves the app. And, the index.html file links other files to it.

We build angular applications with basic concepts which are NgModules. It provides a compilation context for components. At the beginning of an angular project, the command-line interface provides a built-in component which is the root component. But, NgModule can add a number of additional components. These can be created through a template or loaded from a router. This is what a compilation context about.

What is a Component in Angular?

Components are key features in Angular. It controls a patch of the screen called a view. A couple of components that we create on our own helps to build a whole application. In the end, the root component or the app component holds our entire application. The component has its business logic that it does to support the view inside the class. The class interacts with the view through an API of properties and methods. All the components added by us in the application are not linked to the index.html. But, they link to the app.component.html through the selectors. A component can be a component and not only a typescript class by adding a decorator @Component. Then, for further access, a class can import it. The decorator contains some metadata like selector, template, and style. Here’s an example of how a component decorator looks like:

@Component({
    selector: 'app-root',
    templateUrl: 'app.component.html',
    styleUrls: ['app.component.scss']
})

Role of App Module

Modules are the package of functionalities of our app. It gives Angular the information about which features does my app has and what feature it uses. It is an empty Typescript class, but we transform it by adding a decorator @NgModule. So, we have four properties that we set up on the object pass to @NgModule. The four properties are declarations, imports, providers, and bootstrap. All the built-in new components add up to the declarations array in @NgModule.

@NgModule({
declarations: [
  AppComponent,
],
imports: [
  BrowserModule,
  HttpClientModule,
  AppRoutingModule,
  FormsModule
],
bootstrap: [AppComponent]
})

What is Data Binding?

Data Binding is the communication between the Typescript code of the component and the template. So, we have different kinds of data binding given below:

When there is a requirement to output data from our Typescript code in the HTML template. String interpolation handles this purpose like {{data}} in HTML file. Property Binding is also used for this purpose like [property] = “data”.
When we want to trigger any event like clicking a button. Event Binding works while we react to user events like (event) = “expression”.
When we can react to user events and output something at the same time. Two-way Binding is used like [(ngModel)] = “data”.

image for understanding data binding

#angular #javascript #tech blogs #user interface (ui) #angular #angular fundamentals #angular tutorial #basics of angular

Sasha Roberts

1626834660

Angular Rxjs: Use .map() And Async Pipe (Refactor Your Code)

In this video, we will see how to improve our code using the #rxs map operator and #angular #async pipe.

The components should be clean and minimal and should not have code that manipulates the data. Responsible for data manipulation is a service.
The goal is to prepare our data and return an #observable pipe so that we can use an #async pipe in the template.

code: https://github.com/profanis/codeShotsWithProfanis/tree/13/rxjsMapAndAsyncPipe

#angular #rxjs #observable #map #async

#angular rxjs #angular #angular tutorial #what is angular

Urban Cummerata

1595966280

Angular Form Validation

In the last post I introduced angular 2’s model driven form approach. In this post I’m going to go through how to implement validation rules on a model driven form …

Standard validators

At the moment there seem to be 3 standard validators which pretty much do what they say on the tin:

Validators.required
Validators.minLength
Validators.maxLength

Here’s some component code that references the standard required and minLength validators:

export class LoginComponent {
  loginForm: ControlGroup;
  constructor(builder: FormBuilder) {
    this.loginForm = builder.group({
      userName: ["", Validators.required],
      password: ["", Validators.minLength(6)]
    });
  }
}

Multiple validators

You can use Validators.compose to specify multiple validators for a field:

export class LoginComponent {
  loginForm: ControlGroup;
  constructor(builder: FormBuilder) {
    this.loginForm = builder.group({
      userName: ["", Validators.required],
      password: [
        "",
        Validators.compose([Validators.minLength(6), Validators.maxLength(12)])
      ]
    });
  }
}

#angular #standard validators #multiple validators #custom validation

I am Developer

1608866530

Angular 11 Reactive Forms Validation Tutorial

Reactive form validation in Angular 11 app. In this tutorial, i will show you how to use reactive form validation in angular 11 app.

As well as, and you will learn how use reactive form validation in angular 11. And also use reactive form with formGroup for validation in angular 11 app.

Reactive Form Validation In Angular 11
Step 1 – Create New Angular App
Step 2 – Import Form Module
Step 3 – Add Code on View File
Step 4 – Use Component ts File
Step 5 – Start Angular App

https://www.tutsmake.com/angular-11-reactive-forms-validation-tutorial-example/

#reactive form validation in angular 11 #angular 11/10/9/8/7 reactive forms validation example #angular 11 form validation example