Angular- Component

Angular is a framework for developing SPA applications. A SPA application view is made of one or more components. A component represents the view in the Angular application.

Components are the main building block for any Angular application. Each component consists of the following: 

1. HTML template that declares what renders on the page 
2. A TypeScript class that defines the behavior
3. Component Metadata

HTML Template

HTML template is nothing a regular HTML code with angular-specific syntax to communicate with the component class.

Angular - Development Setup

Angular is a JavaScript framework for building web applications. It is maintained by Google and is widely used for creating dynamic single-page applications (SPAs) and complex user interfaces.

In the last post, we get a brief introduction to Angular. In this post, we will follow the steps to set up a development environment for Angular.

1. Install Node.js and npm- Node.js is a runtime environment that allows you to run JavaScript code outside of a web browser. npm is a package manager for Node.js that allows you to install and manage packages and dependencies for your project. To install Node.js and npm, go to the official Node.js website and download the installer for your operating system. Once downloaded, run the installer and follow the on-screen instructions.
2. Install Angular CLI- Angular CLI is a command-line interface tool that helps you create, manage, and deploy Angular projects. To install Angular CLI, open a terminal or command prompt and run the following command-

   npm install -g @angular/cli

Angular- Introduction

What is Angular?

Angular is a JavaScript framework for building web applications. It is maintained by Google and is widely used for creating dynamic single-page applications (SPAs) and complex user interfaces.

Angular provides some powerful features such as two-way data binding, dependency injection, directives, and services that make it easy to build robust and scalable applications.

Below are some features Angular provides-

1. Component-based architecture- Angular is based on a component-based architecture, which allows developers to create reusable, modular components that can be quickly composed into larger applications.
2. Two-way data binding- Angular provides two-way data binding, which allows changes made to the model to be automatically reflected in the view and vice versa. This eliminates the need for complex event handling and makes it easier to keep the view and model in sync.
3. Dependency Injection- Angular's dependency injection system makes it easy to manage dependencies and reduce coupling between components. This helps to improve the maintainability and testability of the application.

Single Page Application (SPA)

What is Single Page Application (SPA)?

A Single Page Application (SPA) is a web application that loads a single HTML page and dynamically updates its content as the user interacts with the application, without requiring a full page reload. 

This approach is different from traditional web applications, where clicking on a link or button would cause the browser to request a new page from the server, which would then be rendered in the browser.

Angular Reactive Form - File validators for File Upload

File upload fuctionality is a very common use case in applications. Whenever we allow users to upload files to server, we should have both client side and server side validation. Most likely we validates file size and file extension.
In this post, we are going to see the validators for File Upload functionality in Aangular Reactive Form.

file-validations.ts

In file-validations.ts, we have three validators- FileExtension validator, FileMaxSize validator and FIle Minimum size validator.

import { AbstractControl, ValidationErrors, ValidatorFn } from '@angular/forms';
const FILE_MAX_SIZE = 2048;
const FILE_MIN_SIZE = 1024;
export class FileValidations {
  public static fileExtensionValidator(
    acceptedExtensions: string[]
  ): ValidatorFn {
    return (control: AbstractControl): ValidationErrors | null => {
      if (control.value) {
        const ext = control.value.split('.').pop();
        if (!acceptedExtensions.includes(ext)) {
          return {
            fileExtension: {
              acceptedExtensions: acceptedExtensions,
              actualExtension: ext,
            },
          };
        }
      }
      return null;
    };
  }
  public static fileMaxSizeValidator(files: FileList): ValidatorFn {
    return (): ValidationErrors | null => {
      if (files.length > 0) {
        if (Math.round(files[0].size / 1024) > FILE_MAX_SIZE) {
          return {
            fileMaxSize: {
              requiredSize: `${Math.round(FILE_MAX_SIZE) / 1024}MB`,
              actualSize: `${Math.round(
                Math.round(files[0].size / 1024) / 1024
              )}MB`,
            },
          };
        }
      }
      return null;
    };
  }
  public static fileMinSizeValidator(files: FileList): ValidatorFn {
    return (): ValidationErrors | null => {
      if (files.length > 0) {
        if (Math.round(files[0].size / 1024) < FILE_MIN_SIZE) {
          return {
            fileMinSize: {
              requiredSize: `${Math.round(FILE_MIN_SIZE) / 1024}MB`,
              actualSize: `${Math.round(
                Math.round(files[0].size / 1024) / 1024
              )}MB`,
            },
          };
        }
      }
      return null;
    };
  }
}