If you are not familiar with classes, don't worry. If we glance at our component file now, we should be mightily impressed with what we have achieved with these 43 lines. Common transpilers include Traceur and Babel. Chandermani Arora is a software craftsman, with a passion for technology and expertise on the web stack. The second tag references a file within our application that sets the configuration for SystemJS. Master the Angular way to structure, build, deploy, and test your code Understand Angular 2's new component-based architecture Build a game and workout runner apps on the Angular platform It starts with a simple 'Guess the Number' game, which serves as a platform to launch you into the world of Angular. Post compilation, it links the view and our component class where changes are synced across the model and viewed in real time as we interact with the app. Within the component, we separate the UI into a view and the behavior into a class, with the appropriate properties and methods needed to support the behavior. Hence, we are going to build our first Hello World app in Angular. The framework then compiles this view template and, in the process, sets up the necessary binding. They provide instructions (called metadata) for the use of our classes. They enable us to combine our components into reusable groups of functionality that can be exported and imported throughout our application. As we mentioned before, this means we will be importing Angular barrels containing multiple modules. As part of this process, each of our TypeScript files will be compiled to a SystemJS module. One of the things Angular boasts about is the ability to have automatic change detection by default, meaning that when an object or object property is changed at runtime, the change will be reflected in the view without having to explicity set up any manual mechanism for doing so. In this case, it converts ES2015 to ES5. This chapter is dedicated to understanding the component pattern and how to put it into practice as we build a simple app using Angular. We'll be covering Angular change detection in depth in Chapter 8, Some Practical Scenarios. Angular 5 released on November 1, 2017, a major feature of which is support for progressive web apps. We touched on app initialization earlier when we created the app.module.ts and main.ts files. Then we call its bootstrapModule method with our AppModule as a parameter. The chapters are structured to introduce the concept, then implement it, and finally explain why it worked. As web applications continue to become more sophisticated, the need to be able to construct them out of smaller and discrete components becomes more compelling. code: The term noOfTries is sandwiched between two interpolation symbols. Our component can use this hidden area to render its display. First, let's look at how we maintain the state in our Angular application. Built with Angular ( It is important to understand that, while Angular uses syntax that has similarities to ES2015 module-loading syntax, Angular modules (which we will discuss a little later in this chapter) are not the same as JavaScript modules. We will discuss how the latter two script tags work together to enable module loading a little later in the chapter. Notice the use of back ticks (introduced by ES2015) for rendering the template string over multiple lines. And putting applications together using self-describing components makes the application easier to understand at a higher level of abstraction. Since we are working with JavaScript, we can put in breakpoints, add a watch, and do everything that is otherwise possible with JavaScript. So, this is the third step in making our component. Getting back to our battery example, the car consumes the battery through a series of connectors. Angular 2 is known for taking the pain out of JavaScript development, and enabling more organized, readable, and testable code.This book builds three apps with varying degrees of complexity. JSFiddle and Plunker: JSFiddle (http://jsfiddle.net/) and Plunker (http://plnkr.co/) are excellent playgrounds for trying out HTML, CSS, and JavaScript code. If it is done right, we can logically organize our application in a way that makes it understandable and easy to maintain. Let's look at the HTML code line that we created for the first of these event bindings. He is also the author for the first edition of this book, AngularJS by Example. He has been building apps on Angular 1 from its early days. To sum up: at a basic level, you will see that to develop applications in Angular, you will do the following: The best way to understand Angular and the component design pattern is by seeing it in action. app, which we built and dissected throughout the chapter. Remember that a lot of errors with code can be detected just by looking at the browser's console window. Sign up to our emails for regular updates, bespoke offers, exclusive This makes GuessTheNumberComponent the root component for our application. We'll ecplore these throughout the examples in this book. In the case of our app package, we indicate that main.ts will be the entry point and ts will be the default extension since we are using TypeScript for it. For example, a battery is a component of an automobile. There are a couple of other places in your code where the ( ) parentheses appear: These two event bindings tie the click events for the buttons on the screen to methods in our component. If you go back to that component you will notice that we added export in front of the class definition, which means we are using module loading within our own application. We'll start by creating a directory for our application. Let's go back to the index.html page again and take a look at the following script tags on this page: The first tag indicates that we will be using a JavaScript library called SystemJS in our application. Optimizing Change Detection in Angular 2 By Example. In addition to this, you will learn about testability and the framework constructs Angular provides to effectively test your app. Then, there is always the Angular source code, a great source of learning. This is called lazy loading, a topic we will cover in Chapter 4, Building Personal Trainer. Designing the component is a very crucial process. In a production application, we would move both these steps into a build process that takes place before the application is launched in the browser. You can install it using Node.js. The Mozilla Developer Network (MDN) describes them as, "syntactical sugar over JavaScript's existing prototype-based inheritance. In order to run our application then, we need something in our application that creates this instance. As the name suggests, this module will provide the functionality needed to run our application in a browser. The @ symbol is used to identify a decorator. If you use the debugger tool in your browser to walk through the application, you will see how change detection works. It supports static typing and class based object oriented programming. Let’s say we want to build a employees application. Templates can be used to make the HTML and CSS inside the Shadow DOM used by our component dynamic. SystemJS follows the ES2015 syntax for module loading and gives us the ability to do module loading in today's browsers. Next, we'll examine something that looks similar to data binding but incorporates an Angular feature we have haven't seen before: structural directives: *ngIf inside the
tags is the NgIf structural directive. It tells us what modules we will be loading and using in our component. We will be discussing this file a little later. TypeScript (which we will discuss next) is also a transpiler, and it is the one that we will use for the examples in this book. While our app has only one component, every Angular application typically starts off with one root component. Now that we have our features, we can determine what we need to display to the user and what data we need to track. Taken together, they offer the opportunity to build a new, forward-looking framework. We next define a new component AppModule. But you only need to add what is required to get the application running and this is what we are doing here. Note that here we are using a custom element based on the Web Components standard. Essentially, it provides instructions to SystemJS as to which modules it should load and directs it to dynamically transpile our TypeScript files to ES5 at runtime. The safe navigation operator is especially helpful in situations where you are loading data asynchronously and it might not be immediately available to the view. Angular does the rest! We will be exploring setting up such a build process in Chapter 2, Building Our First App – 7 Minute Workout. ES2015 adds a new, consistent syntax for loading modules as part of the language. Before we move on there is one other expression that we should touch on: the Angular safe navigation operator (?.). We set these values to null or zero, except for original, in which we use a random number generator to create the number to be guessed. And with this new framework comes a new design pattern—the component pattern. The branch to download for this chapter is GitHub's Branch: checkpoint1.1. For a description of this process by the Angular team, visit https://vsavkin.com/two-phases-of-angular-2-applications-fda2517604be#.fabhc0ynb. Therefore, we are going to build a very simple game called Guess the Number!. Then, using your editor, create a file with the name guess-the-number.component.ts and place it in that subdirectory. This is called change detection, and Angular has a very different approach to doing this than what previously existed. Each Angular application will have one or more modules that contain its components. In the case of Angular, decorators allow us to identify our classes as Angular components. . Angular 2 is known for taking the pain out of JavaScript development, enabling more organized, readable, and testable code. It then assigns that result to NgIf, which will either add the DOM element if the result is true or remove it if it is false. Skip to main content.sg. Transpilation is like compilation, except that instead of converting our code into a machine language as compilation does, transpilation converts one type of source code to another type of source code. We'll name it guessthenumber (but you can name it anything that suits you). If you place a breakpoint at the end of the verifyGuess() method, you will see that when you enter a guess, the noOfTries property is first updated as soon as you hit the breakpoint, like this: Once you move past the breakpoint, the display on the screen updates with the correct number of guesses, as seen in the following screenshot: What is really going on under the hood is that Angular is reacting to events in the application and using change detectors, which go through every component to determine whether anything has changed that affects the view. How does the application decide to display the correct message about whether the guess is correct based on the user input? This will reduce the download size of the application and improve performance. At this point, we will just touch briefly on the bindings that are used in the sample app we are building. You'll also notice that our methods refer to properties in the same class by prepending this to them. You can develop components with ES5, but Angular enhances the ability to develop components by adding support for key features that are found in the latest languages, such as ES2015 and TypeScript. There is one more important tag on the page: This tag is a custom element. As our first exercise, we want to keep things simple but still showcase the framework's capabilities. It looks like standard HTML with some new symbols, such as [ ], ( ), {{, and }}. When they are encapsulated, they do not pollute the global namespace and can interact with other modules in a controlled manner. More Angular 2 SPA Routing and Data Flows in Depth, Computers / Programming Languages / JavaScript, Master the Angular way to structure, build, deploy, and test your code, Understand Angular 2's new component-based architecture, Build a game and workout runner apps on the Angular platform, Design, develop, deploy, and test the apps you build, Work your way through every aspect of app development using Angular2, Understand the inner workings of Angular's view templating and data-binding capabilities, Work on HTML forms and learn the Angular way to bind, validate, and format data, Create component, structural, and attribute directives to extend standard HTML behavior, Integrate with the server backend and find out about data retrieval and persistence using Angular, Gain practical insight into the challenges of building apps using Angular as well as their solutions. https://augury.angular.io/ So, when an expression starts to become complex, move it into a method in your component. Happy coding! The next
