In this tutorial, we introduce you to the NativeScript library, which allows you to create and deploy a web application on a mobile device and use it like a mobile app, rather than as a web or a hybrid application.
[box type=”shadow” align=”” class=”” width=””]The following excerpt is taken from the book TypeScript 2.x By Example written by Sachin Ohri. This book presents essential techniques to leverage the power of TypeScript 2.x to build efficient web applications.[/box]
What is NativeScript?
NativeScript is the open source framework for building native Android and iOS applications with web technologies. This means we can develop native mobile applications with JavaScript, TypeScript, and/or Angular. It is based on the thinking of write once and run everywhere.
Applications developed with NativeScript are pure mobile apps when compared to applications developed with technologies such as PhoneGap. As they are native mobile applications, we can use all the richness of the mobile platform and provide the performance associated with that. We use native APIs and use native controls to render, which allows us to create more sophisticated applications compared to a hybrid approach. Hybrid applications do not provide the same level of flexibility or performance because they are hosted on a separate framework and do not get to interact with low-level mobile APIs directly.
The best part is that it does not require us to learn a new programming language, unlike developing an iOS-based application, for which you need to know Objective C or Swift. So, we can use our existing skills to develop mobile applications.
NativeScript design
NativeScript is a runtime that sits on top of the native mobile operating system and uses the JavaScript Virtual Machine (JVM) V8 on Android and JavaScriptCore on iOS. Having access to these platforms allows NativeScript to expose a unified API system for developers, which is then converted into the native API at runtime.
This translation between the JavaScript APIs and the native platform APIs is possible through reflection, which NativeScript uses to create its own set of interfaces. Another advantage of using JavaScript by NativeScript is its independence from specific editors. You can use any of your favorite editors to develop a NativeScript application, and you will have access to all the native APIs rather than using Xcode for iOS-based apps and Android Studio for Android-based apps.
Architecture
The following is a high-level diagram of NativeScript and its interaction with the mobile platform:
As we can see, the runtime is responsible for converting JavaScript application code to the native platform code. It has various components that work together to convert and call the native APIs. Because NativeScript uses JVM and JavaScriptCore, it has access to all the latest ECMAScript language specifications for development, which allows us to use the latest ES6 feature set.
One of the main components that we need to understand in NativeScript design is modules.
Modules
The NativeScript team made sure that the platform was developed in a modular fashion, much like plugins, which allow us to include only the modules that we need in our development.
These modules provide us with the abstraction of native APIs and allow us to write code that work on both platforms. It has separate APIs for each logical functionality. For example, if you want to use SQLite for your storage needs, there is a package for that; if you want to use a filesystem, there is a package for that.
Let’s take one example to see how these modules help us write consistent code for a multiplatform environment. If you want to access a filesystem on the native platform using NativeScript, you will write code similar to what you see in the following code snippet:
var filesystem = require("file-system");
new filesystem.file(path)
This code is written in pure JavaScript, which first gets a reference to a file-system module, and then, using the API of the file-system module calls a file method. This code, when executed by the NativeScript runtime, first checks the platform it wants to run on and then converts the code accordingly, as shown in the following code snippets.
The Android version of the code will be as follows:
new java.io.file(path)
The iOS version of the code will be as follows:
nsFileManager.defaultManager(); fileManager.createFileAtPathContentsAttributes(path);
If you have worked on any of the mobile platforms before, you will recognize this code as using the native filesystem API to access the file path.
NativeScript versus web applications
Until now, we have been mentioning that we can use our web technologies to write mobile applications with the help of NativeScript. So, can we write a pure web application and use the it in runtime to create a mobile application?
Yes and no. Yes, we can, and we will see with our application that we can use the same code base to write with NativeScript. No, because not all components of web applications can be directly used.
NativeScript allows us to use our existing JavaScript/TypeScript and CSS skills for developing the business logic and the design for our application. But because the native platforms are not web-based and do not have a DOM, we cannot use HTML as the template for our applications. Although you will see that the extension of our template files will be HTML, the element tags will be somewhat different.
To give you a brief example, it does not have UI elements such as <div> or <span>, but has elements such as <StackLayout> and <DockLayout>, which allow us to arrange our UI components.
Another thing to note here is that these UI elements are then converted into native elements based on the platform. So, if we use the <Button> control in NativeScript, it will get converted into android.widget.Button on the Android platform and UIButton on iOS.
Setting up your NativeScript environment
NativeScript provides very good documentation about installing and setting up your development environment. You can find the documentation at https://docs.nativescript.org/angular/start/quick-setup. We will briefly go through the setup process here, but recommend that you go through the documentation to understand the process.
NativeScript CLI
The best way to use is through the NativeScript CLI. You can install it from npm using the following command:
npm install -g nativescript
This command will install the NativeScript library in your global scope. To confirm that the installation has been successful, you can try running the following command from the command-line window:
tns
The tns command is a short form for Telerik NativeScript, and will show the array of commands associated with it.
The NativeScript CLI comes with a host of commands to assist in our development, commands such as create, which helps us create a basic startup project, and deploy, which informs the NativeScript CLI to deploy the application to the device (the device can be a connected device or an emulator). You can check all the commands available with the NativeScript CLI by using the help command as follows:
tns --help
Installing mobile platform dependencies
To build native applications, we need to install the dependencies for those mobile platforms. It is important to remember that if we want to build a NativeScript application for iOS and run it on an iOS-compatible device, we need to use macOS; for building Android applications, we can use both Windows and macOS.
It provides an easy single script for Windows and macOS that takes care of the responsibility to install all the tools and framework required.
The script for Windows is as shown in the following code:
@powershell -NoProfile -ExecutionPolicy Bypass -Command "iex ((new-object net.webclient).DownloadString('https://www.nativescript.org/setup/win'))"
The script for iOS is as shown in the following code:
ruby -e "$(curl -fsSL https://www.nativescript.org/setup/mac)"
It’s important to note that these scripts require administrator-level privileges, so you may need to run them using the sudo command. It also provides a step-by-step guide to installing all these dependencies manually; details can be found at https://docs.nativescript.org/start/ns-setup-win.
Once you have installed all the packages, you can check if the installation was successful by running the following command:
tns doctor
This command checks all the required prerequisites for building a NativeScript application, and if there are no issues identified, this command will return a success message, No issues were detected.
Installing an Android Virtual Device
Once you have installed all the dependencies, the next step is to install an Android emulator, which can be used for testing instead of connecting real devices. To be able to create an emulator, you need to have Android Studio on your machine.
You can install Android Studio from https://developer.android.com/studio/index.html. Once you have installed Android Studio, you can check whether you have the correct Android SDK version. The NativeScript CLI needs Android SDK version 25 or higher; if you see that you do not have the required Android SDK version, then you can install it either using the following command or using the Android Studio IDE:
"%ANDROID_HOME%\tools\bin\sdkmanager" "tools" "platform-tools" "platforms;android-25" "build-tools;25.0.2" "extras;android;m2repository" "extras;google;m2repository"
To install the Android emulator, we use Android Studio, the details of which can be found at https://docs.nativescript.org/tooling/android-virtual-devices.
On macOS, we need to make sure we have hXcodeCode installed, or else, we will not be able to run iOS-based applications.
Again, you can use the tns doctor command to check if your installation was successful.
And that’s it! You have successfully installed and set up the NativeScript environment. Want to learn how to develop native web apps? We’ve got it covered. All you have to do is check out this book TypeScript 2.x By Example to create and deploy web app as a native app in a step-by-step manner.
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Introducing Object Oriented Programmng with TypeScript
Writing SOLID JavaScript code with TypeScript
