include ../../../../_includes/_util-fns :markdown Let's start from zero and build a super simple Angular 2 application in TypeScript. .callout.is-helpful header Don't want TypeScript? :markdown Although we're getting started in TypeScript, you can also write Angular 2 apps in JavaScript and Dart by selecting either of those languages from the combo-box in the banner. .l-main-section :markdown # The shortest, quickest ... Let's put something on the screen in Angular 2 as quickly as we can. .l-sub-section :markdown While we are about to describe steps to take on your development machine, you could take these same steps in an interactive, online coding environment such as [plunker](http://plnkr.co/ "Plunker"). You won't have to install a static server to run the app there. If you like what you see - and we think you will - you can repeat this exercise on your own machine later. :markdown **Create a new folder** to hold our application project, perhaps like this: ``` mkdir angular2-getting-started cd angular2-getting-started ``` ## Our first Angular component **Add a new file** called **`app.ts`** and paste the following lines: +makeExample('gettingstarted/ts/src/app/app.ts', null, 'app.ts') :markdown We've just defined an Angular 2 **component**, one of the most important Angular 2 features. Components are our primary means of creating application views and supporting them with application logic. Ours is an empty, do-nothing class class named `AppComponent`. It would expand with properties and application logic when we're ready to build a substantive application. Above the class we see the `@Component` decoration. .l-sub-section :markdown The `@` symbol before the method name identifies `Component` as a decoration. A "decoration" is a TypeScript language feature for creating metadata about the class. Angular finds this metadata in the transpiled JavaScript and responds appropriately. :markdown `@Component` tells Angular that this class *is an Angular component*. The configuration object passed to the `@Component` method specifies a CSS selector for an HTML element named `my-app`. When Angular sees `my-app`, it will know to create and display an instance of our component. `@View` is another decoration that describes how our component renders on the screen. This one is dead simple, a single line of HTML announcing "My First Angular App". The `bootstrap` line tells Angular to start the application with this component at the application root. We'd be correct to guess that someday our application will consist of more components arising in tree-like fashion from this root. In the top line we imported the `Component`, `View`, and `bootstrap` methods from the Angular 2 library. That's the way we do things now. We no longer expect to find our code or any library code in a global namespace. We `import` exactly what we need, as we need it, from named file and library resources. ## Add `index.html` **Create** an `index.html` file. **Paste** the following lines into it ... and we'll discuss them: +makeExample('gettingstarted/ts/src/index.1.html', null, 'index.html') :markdown We see three noteworthy sections of HTML: 1. We load JavaScript libraries from the web. Let's take them on faith without further discussion.

2. We configure something called `System` and ask it to import the application file with our `AppComponent` that we just wrote. `System` is the module loader (from the `system.js` library), a tool that can `import` code; remember the `import` statement in our `AppComponent`? We're also asking `system.js` to "transpile" (AKA "compile") our TypeScript source code into JavaScript ... right here in the browser.

3. We note the `` tag in the ``. That's the custom HTML element we identified in the `@Component` decoration adorning our `AppComponent` class. ## Run it! We need a static file server to serve our application to the browser. .l-sub-section :markdown Don't have a static file server handy? Let's install one of our favorites called [live-server](https://www.npmjs.com/package/live-server "Live-server"). We'll use the **npm package manager** to install it. Don't have npm? [Go get it](https://docs.npmjs.com/getting-started/installing-node "Installing Node.js and updating npm") because we're going to use it now and repeatedly throughout the guide. Once you have `npm` installed, open a terminal window and enter pre.prettyprint.lang-bash code npm install -g live-server :markdown Open a terminal window and enter pre.prettyprint.lang-bash code live-server :markdown In a few moments, a browser tab should open and display figure.image-display img(src='/resources/images/devguide/getting-started/my-first-app.png' alt="Output of getting started app") :markdown Congratulations! We are in business. .l-main-section :markdown ## What's wrong with this? We were up and running in a hurry and we could explore Angular in this manner for quite some time. For a number of reasons this isn't a good approach for building an application. * Transpiling TypeScript in the browser becomes tediously slow when our app grows beyond a few files. We certainly won't do that in production. We should learn to compile locally and push the generated JavaScript to the server. We'll need some tools for that. * We are writing TypeScript because we want strong-typing and some information about the APIs we're using. If we wrote `AppComponent` in a TypeScript-aware editor, we saw lots of red squiggly lines complaining about our code and we received no guidance about what `Component`, `View`, and `bootstrap` can do. We'll want to load TypeScript definition files to improve our coding experience. * Downloading JavaScript libraries from the web is OK for demos but it slows our development. Every time our app reloads, it must refetch these libraries. Don't count on browser caching. Our debugging and live-reload techniques will bust the browser cache. Loading libraries from the web also prevents us from developing our application offline or where connectivity is poor. Let's learn to download the libraries to our machine and serve them locally. * We want our development cycle to be as fast and friction-free as possible. When we change our code, we want to see the results in the browser immediately. We have tools and procedures for that. .l-main-section :markdown # Upping our game Let's take a few more steps to put our development on a better foundation. We will 1. Revise the application project structure for future growth 1. Install a few tools and packages 1. Prepare for local TypeScript compilation 1. Revise the **`index.html`** to use local library resources 1. Compile the TypeScript locally and watch for changes Shut down the `live-server` running in the terminal window (Ctrl-C) and proceed as follows. .l-main-section :markdown ## Revise the application project structure At the moment we're dumping everything into the "angular2-getting-started" **root folder**. Not bad when there are only two files. Not good as our application evolves. Let's give our project a little structure. We'll add a sub-folder - `src` - to hold project source code and a sub-sub-folder - `src/app` - to hold the application source code. In OS/X and Linux: pre.prettyprint.lang-bash code mkdir src/app :markdown In Windows: pre.prettyprint.lang-bash code mkdir src\app :markdown **Move `index.html`** into the **`src`** folder. **Move `app.ts`** into the **`src/app`** folder. Our project folders should look like this. ``` angular2-getting-started └── src ├── app │ └── app.ts └── index.html ``` .l-main-section :markdown ## Install npm packages locally We'll replace the web-based scripts in our `index.html` with scripts resident on our local machine. We get those scripts by installing two runtime `npm` packages into our project. >**angular.js** - the Angular 2 library. >**system.js** - an open-source library that provides module loading. We'll also install three development tools: >**typescript** - the TypeScript compiler >**tsd** - the [tsd package manager](https://www.npmjs.com/package/tsd "TSD Package Manager") so we can access [TypeScript type definition files](http://definitelytyped.org/ "Definitely Typed") >**[live-server](https://www.npmjs.com/package/live-server "Live-server")** - the static file server that reloads the browser when files change. We may have loaded it earlier. We're doing it again locally in our project so we are no longer vulnerable to a global uninstall or version change. **Open** a terminal window at our application's **root folder** Enter these commands: ``` npm init -y npm i angular2@2.0.0-alpha.39 systemjs@0.19.2 --save --save-exact npm i typescript tsd live-server --save-dev ``` These commands both *install* the packages and *create* an npm `package.json` that will help us develop and maintain our application in future. The essence of our `package.json` should look like this: +makeJson('gettingstarted/ts/package.json', { paths: 'name, version, dependencies, devDependencies'}) :markdown There is also a `scripts` section. **Find and replace** it with the following: +makeJson('gettingstarted/ts/package.json', { paths: 'scripts'}) :markdown We've just extended our project world with script commands that we'll be running very soon. .l-main-section :markdown ## Update `index.html` **Replace** the library scripts section with references to scripts in the packages we just installed. +makeExample('gettingstarted/ts/src/index.html', 'libraries') :markdown **Update** the `System` configuration script as follows. +makeExample('gettingstarted/ts/src/index.html', 'systemjs') .l-sub-section :markdown We won't be transpiling TypeScript in the browser anymore. We'll do that on our machine and ship the generated JavaScript files to the server. We have to re-configure `system.js` to expect JavaScript files with a `.js` extension by default. Someday we might add a `Foo` class to our application in a `foo.ts` file and import it like this pre.prettyprint.lang-bash code import {Foo} from './app/foo' :markdown `system.js`will know to look for a file named `foo.js` in the `src/app` folder. That's exactly what we're doing in the last line. We're importing our main application file `app` (the generated `app.js` to be precise) from the `src/app/` folder (we moved it there, remember?) :markdown Here's the final version +makeExample('gettingstarted/ts/src/index.html', null, 'index.html') .l-main-section :markdown ## Prepare for TypeScript Compilation ### Add links to TypeScript definition files We prefer writing TypeScript apps in editors that understand TypeScript, such as [Visual Studio Code](https://code.visualstudio.com/) and [Web Storm](https://www.jetbrains.com/webstorm/features/). Such editors improve the development experience by checking type information and displaying API documentation ("intellisense") based on TypeScript definition files (`.d.ts`). The definition files we need are included in the npm packages we just installed. We'll use the [**tsd package manager**](https://www.npmjs.com/package/tsd "TSD Package Manager") to generate an *aggregate TypeScript definition file*, **`tsd.d.ts`**, that holds links to the type definition files in those packages. In the ***root* folder** enter the following command (one of the `npm` scripts we added a short while ago) pre.prettyprint.lang-bash code npm run tsd :markdown That produces a new **`src/typings`** folder with the **`tsd.d.ts`** file. Now type-checking and intellisense light up automatically as we write our app in the Visual Studio Code and Web Storm editors. Check your editor's documentation for instructions on using the `tsd.d.ts` file. ### Add the TypeScript configuration file We'll add a configuration file named **`tsconfig.json`** to tell the editor how to interpret our TypeScript code and to simplify the TypeScript compilation command that we'll run very soon. **Change to the `src` folder and create a `tsconfig.json`** file with the following content: +makeJson('gettingstarted/ts/src/tsconfig.json', null, 'tsconfig.json') :markdown Our final project folder structure should look like this: ``` angular2-getting-started ├── node_modules ├── src │ ├── app | │ └── app.ts │ ├── typings │ │ └──tsd.d.ts │ ├── index.html │ └── tsconfig.json └── package.json ``` .l-main-section :markdown ## Compile the TypeScript to JavaScript We no longer transpile TypeScript to JavaScript in the browser. We run the **T**ype**S**cript **C**ompiler (TSC) on our machine instead. Open a terminal window in the **root of the application folder** and enter: pre.prettyprint.lang-bash code npm run tsc :markdown When it's done we should find the generated *app.js* file in the *src* folder and also an *app.map.js* file that helps debuggers navigate between the JavaScript and the TypeScript source. Our script set the compiler watch option (`-w`) so the compiler stays alive when it's finished. It watches for changes to our **`.ts`** files and recompiles them automatically. Leave this command running in the terminal window. You can stop it anytime with `Ctrl-C`. .l-main-section :markdown ## Run the app! Now we are ready to see our app in action. Open another terminal window in the **root of the application folder** and launch `live-server` again although this time we'll do it with one of our `npm` script commands: pre.prettyprint.lang-bash code npm start :markdown **live-server** loads the browser for us, serves the HTML and JavaScript files, and displays our application message once more: figure.image-display img(src='/resources/images/devguide/getting-started/my-first-app.png' alt="Output of getting started app") :markdown ### Make some changes **`live-server`** detects changes to our files and refreshes the browser page for us automatically. Try changing the message to "My SECOND Angular 2 app". The TypeScript compiler in the first terminal window is watching our source code. It recompiles and produces the revised *app.js*. The `live-server` sees that change and reloads the browser. Keep `live-server` running in this terminal window. You can stop it anytime with `Ctrl-C`. .l-main-section :markdown ## What have we done? Our first application doesn't do much. It's basically "Hello, World" for Angular 2. We kept it simple in our first pass: we wrote a little Angular component, we added some JavaScript libraries to `index.html`, and launched with a static file server. That's about all we'd expect to do for a "Hello, World" app. **We have greater ambitions.** We won't ask Angular to build "Hello, World". We are asking it to help us build sophisticated applications with sophisticated requirements. So we made some strategic technology investments to reach our larger goals * our application loads faster with libraries installed locally and we can develop offline if we wish. * we added TypeScript definition files to enhance team productivity and code maintainability. * we're pre-compiling our TypeScript. * we're running the compiler and live-server with commands that give us immediate feedback as we make changes. The good news is that the overhead of setup is (mostly) behind us. We're about to build a small application that demonstrates the great things we can build with Angular 2. Join us next on the [Tour of Heroes].