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 ，和 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. |
Angular is a development platform, built on TypeScript . As a platform, Angular includes:
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.
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.
To install Angular on your local system, you need the following:
engines
key in the
package.json
文件。
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.
Node.js
默认情况下。
To check that you have the npm client installed, run
npm -v
in a terminal window.
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
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
命令：
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.
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.
例如，
app.component.ts
,
app.component.html
，和
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.
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 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
，其中
feature
is the name of your component.
So, you could have files with names such as
header.component.ts
,
signup.component.ts
，或
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.
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
特性：
@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>
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
特性：
@Component({
selector: 'app-root',
templateUrl: './app.component.html',
styles: ['h1 { color: red; }']
})
Typically, a component uses styles in a separate file using the
styleUrls
特性：
@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.
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.
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