TypeScript
Tabris.js 3 targets TypeScript 3.8. TypeScript is a type-safe dialect of JavaScript/EcmaScript and also supports ES6 module syntax (import and export statements) and async/await. A complete guide to TypeScript can be found at typescriptlang.org. As an IDE we can recommend Visual Studio Code with the eslint extension, but there are many suitable TypeScript IDEs out there.
Setup
TypeScript files have to be compiled to JavaScript before execution. The compiler is installed in the project directory to node_modules/.bin/tsc when generating a new Tabris.js app using the tabris init command. (It belongs to the devDependencies in package.json.) To compile the code, simply type npm run build. This also happens when sideloading code via tabris serve, during a full app build via tabris build or on the build service. Alternatively, type tabris serve -w -a to start the compiler in watch mode for incremental compiling. That way you do not have to restart tabris serve after every code change.
If you want to migrate an existing Vanilla-JavaScript Tabris.js project, do the following:
Install TypeScript in your app project:
npm install --save-dev typescript
To configure the TypeScript compiler create a new file called tsconfig.json with the following content:
{
"compilerOptions": {
"module": "commonjs",
"target": "es6",
"outDir": "./dist/",
"lib": [
"es2017"
],
"jsx": "react",
"jsxFactory": "JSX.createElement",
"noImplicitAny": true,
"noImplicitThis": true,
"noUnusedLocals": true,
"noUnusedParameters": true,
"alwaysStrict": true,
"experimentalDecorators": true,
"emitDecoratorMetadata": true,
"allowJs": true,
"sourceMap": true
},
"include": [
"./src/**/*.ts",
"./src/**/*.tsx",
"./src/**/*.js",
"./src/**/*.jsx"
]
}
This is the default configuration for generated TypeScript projects. It includes support for mixed JavaScript/TypeScript projects, JSX and decorators. It also adds some recommended compiler options for stricter TypeScript interpretation. If you do not need any of these, a minimal tsconfig.json would look like this:
{
"compilerOptions": {
"module": "commonjs",
"target": "es6",
"outDir": "./dist/",
"lib": [
"es2017"
]
},
"include": [
"./src/**/*.ts"
]
}
Now edit package.json to let the main field point to the compiled app in dist/:
{
"main": "dist/app.js",
...
}
Also include the following in the scripts sections:
{
"scripts": {
"build": "tsc -p .",
"watch": "tsc -p . -w --preserveWatchOutput",
"start": "tabris serve -a -w"
}
}
The build and watch scripts are called by the Tabris.js CLI to compile the code either once (build) or after every file change (watch).
The start script is optional and provides a shortcut (via npm start) for convenient code sideloading. The -w switch means the watch script is used instead of build, and -a makes the app restart after every re-compile. As a result editing and saving a TypeScript file restarts the app including the code change.
Type Safety
In TypeScript not all APIs, not even all Tabris.js APIs, are perfectly type safe. Here are some guidelines to avoid losing type safety.
Tabris.js specific recommendations:
- Do not use the
widget.on()method. Instead, the Listeners API, e.g.widget.onResize(cb);. - Create type-aware
WidgetCollectioninstances using widget constructors as selectors, e.g.widget.children(Button).first();. - Be aware that while
widget.set()and widget constructors provides auto-completion it does not prevent you from setting non-existing properties. - Use
widget.apply()only to set properties of the baseWidgetclass, likelayoutData. Or avoid it completely.
General TypeScript recommendations:
- Avoid
any. An implicitanymay occur if you do not give a type for a variable, field or parameter, and none can be inferred by assignment. - Avoid explicit casting, Use type guards instead. Tabris.js provides some for
ColorValue, - When using third-party libraries you may have to manually install declaration files to be type safe.
Interfaces
When used in TypeScript the tabris module exports the following additional interfaces:
ImageValue, a union of all types accepted as imagesColorValue, a union of all types accepted as colorsFontValue, a union of all types accepted as fontsPercentValue, a union of all types accepted as percentagesPercentValue, a union of all types accepted as percentagesLinearGradientValue, a union of all types accepted as gradientsSelector, a union of all types accepted as gradientsBoundsTransformationDimension, alias fornumberOffset, alias fornumberBoxDimensionsImageDataAnimationOptionsPropertyChangedEvent<TargetType, ValueType>, same asEventObject<TargetType> & { readonly value: U }- Various
{TargetType}{EventName}Eventinterfaces, e.g.PickerSelectEvent. Only for events with additional parameters. Properties<Widget>, which is the interface of the properties parameter used by the constructor andsetmethod of the given widget.
Developing with Plugins
Plugins expose APIs that aren’t part of the standard JavaScript runtime, so special handling is needed to use them with TypeScript. Regardless of whether an app is built with JavaScript or TypeScript the app needs to have the plugin integrated. When the app is built in debug mode it will have the plugin’s code integrated and will still have the developer console to allow code side-loading, logging and debugging.
For JavaScript projects, global variables are only evaluated at runtime. However, with TypeScript (or those that want code completion in a JavaScript projects) you need type declarations for each plugin. There are three sources for declarations:
From the plugin itself
If the plugin includes typings, the plugin can be added as a dev dependency in your project’s package.json. Because the plugin’s JavaScript/TypeScript code is not being used anywhere in the project, the TypeScript compiler will not automatically include the typings. It is necessary to explicitly include it in your project’s tsconfig.json file, for example:
"include": [
"./src/**/*.ts",
"./src/**/*.tsx",
"./node_modules/cordova.plugins.diagnostic/cordova.plugins.diagnostic.d.ts"
]
From DefinelyTyped
DefinitelyTyped is a repository of community-contributed typings for thousands of packages. Several Cordova plugins have typings available, and they can be installed by adding them to your devDependencies in package.json.
Generating your own
If the plugin does not provide any nor are typings available in DefinitelyTyped you will need to write your own.
The convention for adding globals to a TypeScript project is to place a globals.d.ts or plugins.d.ts file in your project’s src folder. Multiple plugins can have their typings declared in the same file.
If you just want to resolve the compilation warnings and don’t need autocompletion, you can declare them with any. For example, if the plugin provides a global myPlugin variable:
declare var myPlugin: any;
If the plugin attaches to the global cordova object, e.g. cordova.plugins.myPlugin:
interface CordovaPlugins {
myPlugin: any
}
The globals file will automatically become part of your project and there is no need to change tsconfig.json.
Of course it’s always better to add the definitive types (i.e. functions with all the parameters). Note the typings need not provide any functionality beyond satisfying the method’s return type.
