Injector in Angular is a tool used for dependency injection

I have multiple components; I am using Injector in the constructor for encapsulation

import { Component, Injector, OnInit } from '@angular/core';

@Component({
  selector: 'app-base',
  templateUrl: './base.component.html',
  styleUrls: ['./base.component.css'],
})
export class BaseComponent implements OnInit {
  some = '';

  constructor(injector: Injector) {
    this.some = injector.get(this.some);
  }

  ngOnInit(): void {}
}

I'm incorporating BaseComponent into another Component

import { BaseComponent } from '../base/base.component';

@Component({
  selector: 'app-base-state',
  templateUrl: './base-state.component.html',
  styleUrls: ['./base-state.component.css'],
})
export class BaseStateComponent extends BaseComponent implements OnInit {
  constructor(injector: Injector) {
    super(injector);
  }

  ngOnInit(): void {}
}

I intend to use BaseStateComponent in other components; The question arises: Is there a way to make the injector in BaseComponent or BaseStateComponent optional? There are instances where I need a component without requiring its injector;

I am aware of the @Optional() and @Self() features

constructor(@Optional(), @Self()); 

However, I find it challenging to understand how these decorators work. I would appreciate if someone could explain them;

stack

Answer №1

Your dilemma arises from the desire to utilize @Optional @Self in order to make the injector optional. However, it is important to note that @optional @self functions effectively with entities that are considered injectable, which can be specified within the providers array at a certain level. In the context of Angular, services are inherently injectable, allowing for the utilization of @Optional @Self @SkipSelf with services or other injectable elements.

Upon implementing the constrocutor(private someService:SomeService), Angular will verify whether the provision of SomeService occurs on the component level within the @component's list of providers. If not, it delves into checking if the service is provided at the Module Level or ultimately at the Root level, encompassing an examination of the entire Injector tree.

The use of @Optional circumvents this verification process and so forth...

A crucial point to remember is that Injector resolves a token to a dependency.

Answering your query:

To implement an optional parameter approach in typescript, you simply affix a ? next to the parameter as illustrated below,

export class BaseComponent implements OnInit {
  some = '';
  
  constructor(private injector?: Injector) {             // ? signifies parameter's optionality
    this.some = injector.get(this.some);
  }
  
  ngOnInit(): void {}
}

This rationale aligns well with OOP principles implemented through classes.

Modified Stackblitz Version (Resolving additional issues as well)

Similar questions

If you have not found the answer to your question or you are interested in this topic, then look at other similar questions below or use the search

What is the best way to manage multiple data operations simultaneously using ngrx?

In collaboration with the entirety of the "flux architecture" (actions, effects, reducers, etc.) along with rxjs, my aim is to create and delete multiple data. However, I am facing the following challenges: How can I create or delete multiple data in bo ...

What is the method for entering text into a span element and submitting it by hitting the "ENTER" key using Selenium in Python 3.7?

Environment: Using Python 3.7 and Selenium 3.141 Issue : I need to automate commenting on posts using Selenium in a web page. The challenge is that the comment form does not have a traditional "Submit" button; instead, it's a SPAN element where yo ...

Displaying a table using Vue.js to showcase filtered data fetched with Axios

I have been struggling to find a solution for displaying filtered results in my table using Vue.js and Axios. While I am able to filter the results with an if statement, the issue arises when exporting the data as it includes unfiltered results as well. Cu ...

Display the original content of a previous div element after modifying it using JavaScript

I wanted to simplify the code. In my jsp file, when the document is loaded, the select values are filled in automatically. For instance: <div class="col-sm"> <label style="font-size: 20px;"><fmt:message key="cap.workplace"/>: </ ...

What could be causing this JSON object error I'm experiencing?

res.send({ customerDetails:{ fName, lName, }, applicantDetails:{ [ {primaryApplicant:{fName1,lName1}}, {secondaryApplicant:{fName2,lName2}}, {thirdA ...

What is the best way to display HTML content inside a pop-over window?

How can I load popover content from another HTML file using templateUrl in AngularJS? Check out the demo below: HTML: <!DOCTYPE html> <html ng-app="plunker"> <head> <meta charset="utf-8"/> <title>AngularJS Plunker& ...

I am having trouble printing because of document.write

Whenever I use javascript to create a document with document.write I include an iframe element then I try to print the contents using iframe.print() but nothing happens - no error message and no print dialog box. How can I successfully initiate a print ...

Sending an AJAX request will only transmit a portion of an array when using the JSON.stringify

I have a JavaScript array that is constantly updated. Here's how I initially set up the array... columnArray = ["userID", "Date", "trialType", "cue", "target", "response", "accuracy", "lenAcc", "strictAcc", "fkpl", "totalTime"]; var dataArray = []; ...

When employing useNavigation, the URL is updated but the component does not render or appear on the

Check out this code snippet: https://codesandbox.io/p/sandbox/hardcore-lake-mptzw3 App.jsx: import ContextProvider from "./provider/contextProvider"; import Routes from "./routes"; function App() { console.log("Inside App" ...

Change the API endpoint for webpack in production

In my Angular 4 project, I am utilizing webpack to manage the API url. However, for production, I need to specify a different API url. Can anyone guide me on where exactly I should input the new url in my jhipster project? Source: webpack.prod.js : ...

What is the best way to save a Firebase user's unique identifier in a React application?

In the process of developing a React web application, I am focusing on allowing users to register using their email and password. Once registered, each user will have access to their profile information. I have outlined my Firebase data structure below: ...

A reflective key error has occurred because the token was not properly defined!

My current setup includes Angular version 2.4.4. However, I encountered an issue when trying to declare a service resolver and register it in both the component module and router. import { Injectable } from '@angular/core'; import { Resolve, Ac ...

Exploring the use of a customizable decorator in Typescript for improved typing

Currently, I am in the process of creating TypeScript typings for a JavaScript library. One specific requirement is to define an optional callable decorator: @model class User {} @model() class User {} @model('User') class User {} I attempted ...

The process of registering with JWT tokens and the challenge that arises when a token expires

I had the idea to implement a registration process that requires users to provide their username, email (which must not already exist in the database), password, and confirm password. The project is built using NextJS with pages router and Typescript. impo ...

Sending an Ajax request using an array of parameters and then accessing them in PHP

I have created a JavaScript function that facilitates AJAX posts by accepting an array of parameters. The function is outlined below: /** * A quick function to execute an AJAX call with POST method and retrieve data in JSON format * @param {string} url - ...

Error encountered during Angular boot process due to npm running lifecycle script ELIFECYCLE

I encountered an issue while trying to boot up my Angular project. I attempted to install necessary plugins, but ran into some errors. { "name": "portal-app", "version": "0.0.0", "license": "MIT", "scripts": { "ng": "ng", "start": "ng ser ...

Retrieve the total number of hours within a designated time frame that falls within a different time frame

Having a difficult time with this, let me present you with a scenario: A waiter at a restaurant earns $15/hour, but between 9:00 PM and 2:30 AM, he gets paid an additional $3/hour. I have the 'start' and 'end' of the shift as Date obje ...

What is the best way to save a parsed JSON value to a variable in Express?

I am currently utilizing the body-parser module to parse incoming JSON objects within a POST request. My goal is to extract and store a specific value from the JSON data into a variable for later database insertion. Below is a fragment of the code: var h ...

Utilizing numbered lists through HTML, CSS, and/or JavaScript

I am looking to accomplish something similar to this... My guess is that the images should be stored in an array in Javascript with the image links. However, I am uncertain if this can be done using only HTML and CSS. I found a solution on this thread, w ...

What is the best method to find a matching property in one array from another?

I am working with two arrays in TypeScript. The first one is a products array containing objects with product names and IDs, like this: const products = [ { product: 'prod_aaa', name: 'Starter' }, { product: 'prod_bbb&apos ...