Automatically injecting dependencies in Aurelia using Typescript

Question

Automatically injecting dependencies in Aurelia using Typescript

Recently, I started working with Typescript and Aurelia framework. Currently, I am facing an issue while trying to implement the @autoinject decorator in a VS2015 ASP.NET MVC 6 project.

Below is the code snippet I am using:

import {autoinject} from "aurelia-framework";
import {HttpClient} from "aurelia-http-client";

@autoinject()
export class App {
       http: HttpClient;
       constructor(httpClient: HttpClient) {
          this.http = httpClient;
       }

       activate() {
          this.http.get("/api/test/")...
       }
}

Upon running this code, I encounter an error stating that 'this.http' is undefined.

I suspect that enabling TypeScript's emitDecoratorMetadata flag could resolve this issue, but I am unsure on how to do so.

I attempted adding a tsconfig.json file to the project and setting the flag in compiler options, however, it resulted in multiple errors (duplicate identifier). How can I address these errors? Is there something specific I need to include under "files"?

Additionally, here is my config.js file for reference:

System.config({
  baseURL: "/",
  defaultJSExtensions: true,
  transpiler: "typescript",
  paths: {
    "npm:*": "jspm_packages/npm/*",
    "github:*": "jspm_packages/github/*"
  },

  map: {
    "aurelia-bootstrapper": "npm:<a href="/cdn-cgi/l/email-protection" class="__cf_email__" data-cfemail="e584909780898c84c8878a8a919691978495958097a5d4cbd5cbd5c887809184cbd4">[email protected]</a>",
    "aurelia-framework": "npm:<a href="/cdn-cgi/l/email-protection" class="__cf_email__" data-cfemail="1574606770797c74387367747870627a677e55243b253b2538777061743b243b253b22">[email protected]</a>",
    "aurelia-http-client": "npm:<a href="/cdn-cgi/l/email-protection" class="__cf_email__" data-cfemail="ee8f9b9c8b82878fc3869a9a9ec38d82878b809aaedfc0dec0dec38c8b9a8fc0df">[email protected]</a>",
    "typescript": "npm:<a href="/cdn-cgi/l/email-protection" class="__cf_email__" data-cfemail="84f0fdf4e1f7e7f6edf4f0c4b5aab3aab1">[email protected]</a>",
     ....
  }
});

javascript typescript aurelia

Answer 1

Answer №1

Understanding the Functionality of @autoInject()

Prior to utilizing TypeScript's emitDecoratorMetadata flag, it is important to note that this setting enables the TypeScript compiler to introduce the Metadata Reflection API and incorporate a unique decorator definition into the transpiled TypeScript code.

With Aurelia's @autoInject() decorator, it leverages the type metadata generated by TypeScript's decorator mechanism and applies it to the respective class similar to how the @inject(...) decorator functions.

To implement this feature, ensure to activate the new option within the compilerOptions section of your Type Script configuration.

TypeScript Configuration Sample:

{
    "version": "1.5.1",
    "compilerOptions": {
        "target": "es5",
        "module": "amd",
        "declaration": false,
        "noImplicitAny": false,
        "removeComments": false,
        "noLib": true,
        "emitDecoratorMetadata": true
    },
    "filesGlob": [
        "./**/*.ts",
        "!./node_modules/**/*.ts"
    ],
    "files": [
        // ...
    ]
}

Snippet Screenshot from Related Article:

https://i.sstatic.net/AvFbM.jpg

Further Reading on emitDecoratorMetadata:

Explore Available Type Script Options:
https://github.com/Microsoft/TypeScript/wiki/Compiler-Options

If desired, Gulp-Typescript offers a viable solution along with relevant Gulp settings

Gulp Supported Options: https://github.com/ivogabe/gulp-typescript#options
GitHub Discussion Thread: https://github.com/ivogabe/gulp-typescript/issues/100

Sample Gulp Code Snippet: gulp.task('build-ts', [], function() {

  return gulp.src(paths.typescript)
    .pipe(plumber())
    .pipe(changed(paths.output, {extension: '.js'}))
    .pipe(sourcemaps.init())
    .pipe(ts({
      declarationFiles: false,
      noExternalResolve: true,
      target: 'es5',
      module: 'commonjs',
      emitDecoratorMetadata: true,
      typescript: typescript
    }))
    .pipe(sourcemaps.write())
    .pipe(gulp.dest(paths.output));
});

Answer 2

Understanding the Functionality of @autoInject()

Prior to utilizing TypeScript's emitDecoratorMetadata flag, it is important to note that this setting enables the TypeScript compiler to introduce the Metadata Reflection API and incorporate a unique decorator definition into the transpiled TypeScript code.

With Aurelia's @autoInject() decorator, it leverages the type metadata generated by TypeScript's decorator mechanism and applies it to the respective class similar to how the @inject(...) decorator functions.

To implement this feature, ensure to activate the new option within the compilerOptions section of your Type Script configuration.

TypeScript Configuration Sample:

{
    "version": "1.5.1",
    "compilerOptions": {
        "target": "es5",
        "module": "amd",
        "declaration": false,
        "noImplicitAny": false,
        "removeComments": false,
        "noLib": true,
        "emitDecoratorMetadata": true
    },
    "filesGlob": [
        "./**/*.ts",
        "!./node_modules/**/*.ts"
    ],
    "files": [
        // ...
    ]
}

Snippet Screenshot from Related Article:

https://i.sstatic.net/AvFbM.jpg

Further Reading on emitDecoratorMetadata:

Explore Available Type Script Options:
https://github.com/Microsoft/TypeScript/wiki/Compiler-Options

If desired, Gulp-Typescript offers a viable solution along with relevant Gulp settings

Gulp Supported Options: https://github.com/ivogabe/gulp-typescript#options
GitHub Discussion Thread: https://github.com/ivogabe/gulp-typescript/issues/100

Sample Gulp Code Snippet: gulp.task('build-ts', [], function() {

  return gulp.src(paths.typescript)
    .pipe(plumber())
    .pipe(changed(paths.output, {extension: '.js'}))
    .pipe(sourcemaps.init())
    .pipe(ts({
      declarationFiles: false,
      noExternalResolve: true,
      target: 'es5',
      module: 'commonjs',
      emitDecoratorMetadata: true,
      typescript: typescript
    }))
    .pipe(sourcemaps.write())
    .pipe(gulp.dest(paths.output));
});

Answer 3

Answer №2

Exploring the @autoinject & @inject Decorators

If you're curious about what exactly the @autoinject and @inject decorators contain, look no further than the dependency-injection Library within the popular aurelia Framework.

    /**
    * Dive into the TypeScript transpiler behavior with this decorator
    */
    export function autoinject(potentialTarget?: any): any {
      let deco = function(target) {
        target.inject = metadata.getOwn(metadata.paramTypes, target) || _emptyParameters;
      };

      return potentialTarget ? deco(potentialTarget) : deco;
    }

    /**
    * Define the dependencies to be injected by the DI Container
    */
    export function inject(...rest: any[]): any {
      return function(target, key, descriptor) {
        // Check if we are injecting into a method or constructor
        if (descriptor) {
          const fn = descriptor.value;
          fn.inject = rest;
        } else {
          target.inject = rest;
        }
      };
    }

For more information, check out the Source URL: https://github.com/aurelia/dependency-injection/blob/master/src/injection.js

Answer 4

Exploring the @autoinject & @inject Decorators

If you're curious about what exactly the @autoinject and @inject decorators contain, look no further than the dependency-injection Library within the popular aurelia Framework.

    /**
    * Dive into the TypeScript transpiler behavior with this decorator
    */
    export function autoinject(potentialTarget?: any): any {
      let deco = function(target) {
        target.inject = metadata.getOwn(metadata.paramTypes, target) || _emptyParameters;
      };

      return potentialTarget ? deco(potentialTarget) : deco;
    }

    /**
    * Define the dependencies to be injected by the DI Container
    */
    export function inject(...rest: any[]): any {
      return function(target, key, descriptor) {
        // Check if we are injecting into a method or constructor
        if (descriptor) {
          const fn = descriptor.value;
          fn.inject = rest;
        } else {
          target.inject = rest;
        }
      };
    }

For more information, check out the Source URL: https://github.com/aurelia/dependency-injection/blob/master/src/injection.js

Automatically injecting dependencies in Aurelia using Typescript

Answer №1

Understanding the Functionality of @autoInject()

Answer №2

Exploring the @autoinject & @inject Decorators

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