Getting started with Angular

It is now time to look at Google's Angular framework, another popular option that you'll come across often. In this article we look at what Angular has to offer, install the prerequisites and set up a sample app, and look at Angular's basic architecture.

Prerequisites:	Familiarity with the core HTML, CSS, and JavaScript languages, knowledge of the terminal/command line.
Objective:	To setup a local Angular development environment, create a starter app, and understand the basics of how it works.

What is Angular?

Angular is a development platform, built on TypeScript. As a platform, Angular includes:

A component-based framework for building scalable web applications
A collection of well-integrated libraries that cover a wide variety of features, including routing, forms management, client-server communication, and more
A suite of developer tools to help you develop, build, test, and update your code

When you build applications with Angular, you're taking advantage of a platform that can scale from single-developer projects to enterprise-level applications. Angular is designed to make updating as easy as possible, so you can take advantage of the latest developments with a minimum of effort. Best of all, the Angular ecosystem consists of a diverse group of over 1.7 million developers, library authors, and content creators.

Before you start exploring the Angular platform, you should know about the Angular CLI. The Angular CLI is the fastest, easiest, and recommended way to develop Angular applications. The Angular CLI makes a number of tasks easy. Here are some examples:

`ng build`	Compiles an Angular app into an output directory.
`ng serve`	Builds and serves your application, rebuilding on file changes.
`ng generate`	Generates or modifies files based on a schematic.
`ng test`	Runs unit tests on a given project.
`ng e2e`	Builds and serves an Angular application, then runs end-to-end tests.

You'll find the Angular CLI to be a valuable tool for building out your applications.

What you'll build

This tutorial series guides you through building a to-do list application. Via this application you'll learn how to use Angular to manage, edit, add, delete, and filter items.

Prerequisites

To install Angular on your local system, you need the following:

Node.js Angular requires a current, active LTS, or maintenance LTS version of Node.js. For information about specific version requirements, see the engines key in the package.json file. For more information on installing Node.js, see nodejs.org. If you are unsure what version of Node.js runs on your system, run node -v in a terminal window.
npm package manager Angular, the Angular CLI, and Angular applications depend on npm packages for many features and functions. To download and install npm packages, you need an npm package manager. This guide uses the npm client command line interface, which is installed with Node.js by default. To check that you have the npm client installed, run npm -v in a terminal window.

Set up your application

You can use the Angular CLI to run commands in your terminal for generating, building, testing, and deploying Angular applications. To install the Angular CLI, run the following command in your terminal:

npm install -g @angular/cli

Angular CLI commands all start with ng, followed by what you'd like the CLI to do. In the Desktop directory, use the following ng new command to create a new application called todo:

ng new todo --routing=false --style=css

The ng new command creates a minimal starter Angular application on your Desktop. The additional flags, --routing and --style, define how to handle navigation and styles in the application. This tutorial describes these features later in more detail.

If you are prompted to enforce stricter type checking, you can respond with yes.

Navigate into your new project with the following cd command:

cd todo

To run your todo application, use ng serve:

ng serve

When the CLI prompts you about analytics, answer no.

In the browser, navigate to http://localhost:4200/ to see your new starter application. If you change any of the source files, the application automatically reloads.

While ng serve is running, you might want to open a second terminal tab or window in order to run commands. If at any point you would like to stop serving your application, press Ctrl+c while in the terminal.

Get familiar with your Angular application

The application source files that this tutorial focuses on are in src/app. Key files that the CLI generates automatically include the following:

app.module.ts: Specifies the files that the application uses. This file acts as a central hub for the other files in your application.
app.component.ts: Also known as the class, contains the logic for the application's main page.
app.component.html: Contains the HTML for AppComponent. The contents of this file are also known as the template. The template determines the view or what you see in the browser.
app.component.css: Contains the styles for AppComponent. You use this file when you want to define styles that only apply to a specific component, as opposed to your application overall.

A component in Angular is made up of three main parts—the template, styles, and the class. For example, app.component.ts, app.component.html, and app.component.css together constitute the AppComponent. This structure separates the logic, view, and styles so that the application is more maintainable and scalable.

In this way, you are using the best practices from the very beginning.

The Angular CLI also generates a file for component testing called app.component.spec.ts, but this tutorial doesn't go into testing, so you can ignore that file.

Whenever you generate a component, the CLI creates these four files in a directory with the name you specify.

The structure of an Angular application

Angular is built with TypeScript. TypeScript is a superset of JavaScript meaning that any valid JavaScript is valid TypeScript. TypeScript offers typing and a more concise syntax than plain JavaScript, which gives you a tool for creating more maintainable code and minimizing bugs.

Components are the building blocks of an Angular application. A component includes a TypeScript class that has a @Component() decorator, an HTML template, and styles.

The class

The class is where you put any logic your component needs. This code can include functions, event listeners, properties, and references to services to name a few. The class is in a file with a name such as feature.component.ts, where feature is the name of your component. So, you could have files with names such as header.component.ts, signup.component.ts, or feed.component.ts. You create a component with a @Component() decorator that has metadata that tells Angular where to find the HTML and CSS. A typical component is as follows:

import { Component } from '@angular/core';

@Component({
  selector: 'app-item',
    // the following metadata specifies the location of the other parts of the component
  templateUrl: './item.component.html',
  styleUrls: ['./item.component.css']
})

export class ItemComponent {
// your code goes here
}

This component is called ItemComponent, and its selector is app-item. You use a selector just like regular HTML tags by placing it within other templates. When a selector is in a template, the browser renders the template of that component. This tutorial guides you through creating two components and using one within the other.

Angular's component model offers strong encapsulation and an intuitive application structure. Components also make your application easier to unit test and can improve the overall readability of your code.

The HTML template

Every component has an HTML template that declares how that component renders. You can define this template either inline or by file path.

To refer to an external HTML file, use the templateUrl property:

@Component({
  selector: 'app-root',
  templateUrl: './app.component.html'
})

export class AppComponent {
}

To write inline HTML, use the template property and write your HTML within backticks:

@Component({
  selector: 'app-root',
  template: `<h1>Hi!</h1>`,
})

export class AppComponent {
}

Angular extends HTML with additional syntax that lets you insert dynamic values from your component. Angular automatically updates the rendered DOM when your component's state changes. One use of this feature is inserting dynamic text, as shown in the following example.

<h1>{{ title }}</h1>

The double curly braces instruct Angular to interpolate the contents within them. The value for title comes from the component class:

import { Component } from '@angular/core';

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

export class AppComponent {
    title = 'To do application';
}

When the application loads the component and its template, the browser sees the following:

<h1>To do application</h1>

Styles

A component can inherit global styles from the application's styles.css file and augment or override them with its own styles. You can write component-specific styles directly in the @Component() decorator or specify the path to a CSS file.

To include the styles directly in the component decorator, use the styles property:

@Component({
  selector: 'app-root',
  templateUrl: './app.component.html',
  styles: ['h1 { color: red; }']
})

Typically, a component uses styles in a separate file using the styleUrls property:

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

With component-specific styles, you can organize your CSS so that it is easily maintainable and portable.

Summary

That's it for your first introduction to Angular. At this point you should be set up and ready to build an Angular app, and have a basic understanding of how Angular works. In the next article we'll deepen that knowledge and start to build up the structure of our to-do list application.