xref: /docs/en/application-dev/quick-start/start-with-js-fa.md

# Building the First JavaScript Application in FA Model


> **NOTE**
>
> For best possible results, use [DevEco Studio 3.1 Beta2](https://developer.harmonyos.com/cn/develop/deveco-studio#download) for your development.


## Creating a JavaScript Project

1. If you are opening DevEco Studio for the first time, click **Create Project**. If a project is already open, choose **File** > **New** > **Create Project** from the menu bar. On the **Choose Your Ability Template** page, select **Application** (or **Atomic Service**, depending on your project), select **Empty Ability** as the template, and click **Next**.

   ![createProject](figures/createProject.png)

2. In the project configuration page, set **Compile SDK** to **8** or **9** (in the latter case, you also need to set **Model** to **FA**) and **Language** to **JS** and retain the default values for other parameters.

   ![chooseFAModel_js](figures/chooseFAModel_js.png)

   > **NOTE**
   >
   > If you are using DevEco Studio V2.2 Beta1 or later, you can use the low-code development mode apart from the traditional coding approach.
   >
   > On the low-code development pages, you can design your application UI in an efficient, intuitive manner, with a wide array of UI editing features.
   >
   > To use the low-code development mode, turn on **Enable Super Visual** on the page shown above.

3. Click **Finish**. DevEco Studio will automatically generate the sample code and resources that match your project type. Wait until the project is created.

4. After the project is created, in the **entry** > **build-profile.json5** file, change **runtimeOS** under **targets** to **OpenHarmony**, and click **Sync Now** in the upper right corner to start development.


## JavaScript Project Directory Structure

![en-us_image_0000001435376433](figures/en-us_image_0000001435376433.png)

- **entry**: OpenHarmony project module, which can be built into an OpenHarmony Ability Package ([HAP](../../glossary.md#hap)).
  - **src > main > js**: a collection of JavaScript source code.
  - **src > main > js > MainAbility**: entry to your application/service.
  - **src > main > js > MainAbility > i18n**: resources in different languages, for example, UI strings and image paths.
  - **src > main > js > MainAbility > pages**: pages contained in **MainAbility**.
  - **src > main > js > MainAbility > app.js**: ability lifecycle file.

  - **src > main > resources**: a collection of resource files used by your application/service, such as graphics, multimedia, character strings, and layout files. For details about resource files, see [Resource Limitations and Access](../ui/js-framework-resource-restriction.md).
  - **src > main > config.json**: module configuration file. This file describes the global configuration information of the application/service, the device-specific configuration information, and the configuration information of the HAP file. For details, see [Application Configuration File Overview (FA Model)](application-configuration-file-overview-fa.md).
  - **build-profile.json5**: current module information and build configuration options, including **buildOption** and **targets**. Under **targets**, you can set **runtimeOS** to **HarmonyOS** (default) or **OpenHarmony**, depending on the OS of your application.
  - **hvigorfile.ts**: module-level build script. You can customize related tasks and code implementation.

- **build-profile.json5**: application-level configuration information, including the signature and product configuration.

- **hvigorfile.ts**: application-level build script.


## Building the First Page

1. Use the **\<Text>** component.

   After the project synchronization is complete, choose **entry** > **src** > **main** > **js** > **MainAbility** > **pages** > **index** in the **Project** window and open the **index.hml** file. You can see that the file contains a **<Text>** component. The sample code in the **index.hml** file is shown below:

   ```html
   <!-- index.hml -->
   <div class="container">
       <text class="title">
           Hello World
       </text>
   </div>
   ```

2. Add a button and bind the **onclick** method to this button.

   On the default page, add a **\<Button>** component to respond to user clicks and implement redirection to another page. The sample code in the **index.hml** file is shown below:

   ```html
   <!-- index.hml -->
   <div class="container">
       <text class="title">
           Hello World
       </text>

   <!-- Add a button, set its value to Next, and bind the onclick method to the button. -->
       <input class="btn" type="button" value="Next" onclick="onclick"></input>
   </div>
   ```

3. Set the page style in the **index.css** file.

   From the **Project** window, choose **entry** > **src** > **main** > **js** > **MainAbility** > **pages** > **index**, open the **index.css** file, and set the page styles, such as the width, height, font size, and spacing. The sample code in the **index.css** file is shown below:

   ```css
   /* index.css */
   .container {
       display: flex;
       flex-direction: column;
       justify-content: center;
       align-items: center;
       left: 0px;
       top: 0px;
       width: 100%;
       height: 100%;
   }

   .title {
       font-size: 100px;
       font-weight: bold;
       text-align: center;
       width: 100%;
       margin: 10px;
   }

   .btn {
       font-size: 60px;
       font-weight: bold;
       text-align: center;
       width: 40%;
       height: 5%;
       margin-top: 20px;
   }
   ```

4. On the toolbar in the upper right corner of the editing window, click **Previewer**. Below is how the first page looks in the Previewer.

   ![en-us_image_0000001311494592](figures/en-us_image_0000001311494592.png)


## Building the Second Page

1. Create the second page.

   In the **Project** window, choose **entry** > **src** > **main** > **js** > **MainAbility**, right-click the **pages** folder, choose **New** > **Page**, name the page **second**, and click **Finish**. Below is the structure of the **second** folder.

   ![en-us_image_0000001311334944](figures/en-us_image_0000001311334944.png)

2. Add **\<Text>** and **\<Button>** components.

   Add **\<Text>** and **\<Button>** components and set their styles, as you do for the first page. The sample code in the **second.hml** file is shown below:

   ```html
   <!-- second.hml -->
   <div class="container">
       <text class="title">
           Hi there
       </text>

   <!-- Add a button, set the value to Back, and bind the back method to the button.-->
       <input class="btn" type="button" value="Back" onclick="back"></input>
   </div>
   ```

3. Set the page style. The sample code in the **second.css** file is shown below:

   ```css
   /* second.css */
   .container {
       display: flex;
       flex-direction: column;
       justify-content: center;
       align-items: center;
       left: 0px;
       top: 0px;
       width: 100%;
       height: 100%;
   }

   .title {
       font-size: 100px;
       font-weight: bold;
       text-align: center;
       width: 100%;
       margin: 10px;
   }

   .btn {
       font-size: 60px;
       font-weight: bold;
       text-align: center;
       width: 40%;
       height: 5%;
       margin-top: 20px;
   }
   ```


## Implementing Page Redirection

You can implement page redirection through the [page router](../reference/apis/js-apis-router.md), which finds the target page based on the page URL. Import the **router** module and then perform the steps below:

1. Implement redirection from the first page to the second page.

   In the **index.js** file of the first page, bind the **onclick** method to the button so that clicking the button redirects the user to the second page. The sample code in the **index.js** file is shown below:

   ```js
   // index.js
   // Import the router module.
   import router from '@ohos.router';

   export default {
       onclick: function () {
           router.push({
               url: "pages/second/second"
           })
       }
   }
   ```

2. Implement redirection from the second page to the first page.

   In the **second.ets** file of the second page, bind the **back** method to the **Back** button so that clicking the button redirects the user back to the first page. The sample code in the **second.js** file is shown below:

   ```js
   // second.js
   // Import the router module.
   import router from '@ohos.router';

   export default {
       back: function () {
           router.back()
       }
   }
   ```

3. Open any file in the **index** folder and click ![en-us_image_0000001311015192](figures/en-us_image_0000001311015192.png) in the Previewer to refresh the file. The display effect is shown in the figure below.

   ![en-us_image_0000001311175132](figures/en-us_image_0000001311175132.png)


## Running the Application on a Real Device

1. Connect the development board running the OpenHarmony standard system to the computer.

2. Choose **File** > **Project Structure...** > **Project** > **Signing Configs**, and select **Automatically generate signature**. Wait until the automatic signing is complete, and click **OK**. See the following figure.

   ![signConfig](figures/signConfig.png)

3. On the toolbar in the upper right corner of the editing window, click ![en-us_image_0000001364054485](figures/en-us_image_0000001364054485.png). The display effect is shown in the figure below.

   ![en-us_image_0000001311175132](figures/en-us_image_0000001311175132.png)

Congratulations! You have finished developing your OpenHarmony application in JavaScript in the FA model. To learn more about OpenHarmony application development, see [Application Development Overview](../application-dev-guide.md).