The ngOnInit function is not triggered upon instantiation of an Injectable class

Question

The ngOnInit function is not triggered upon instantiation of an Injectable class

What could be causing the ngOnInit() method not to be called upon resolution of an Injectable class?

Code

import {Injectable, OnInit} from 'angular2/core';
import { RestApiService, RestRequest } from './rest-api.service';

@Injectable()
export class MovieDbService implements OnInit {

    constructor(private _movieDbRest: RestApiService){
        window.console.log('FROM constructor()');
    }

    ngOnInit() {
         window.console.log('FROM ngOnInit()');
    }

}

Console Output

FROM constructor()

javascript angular typescript

Answer 1

Answer №1

Lifecycle hooks, such as OnInit(), are designed to work specifically with Directives and Components. They do not function with other types, like a service in this particular scenario. According to the documentation:

A Component's lifecycle is managed by Angular itself. Angular creates it, renders it, creates and renders its children, checks it when its data-bound properties change, and destroys it before removing it from the DOM.

Directive and component instances follow a lifecycle where Angular creates, updates, and eventually destroys them.

Answer 2

Lifecycle hooks, such as OnInit(), are designed to work specifically with Directives and Components. They do not function with other types, like a service in this particular scenario. According to the documentation:

A Component's lifecycle is managed by Angular itself. Angular creates it, renders it, creates and renders its children, checks it when its data-bound properties change, and destroys it before removing it from the DOM.

Directive and component instances follow a lifecycle where Angular creates, updates, and eventually destroys them.

Answer 3

Answer №2

While I may not have all the details on every lifecycle hook, I do know that when it comes to destruction, ngOnDestroy is called for Injectable when its provider is destroyed (such as an Injectable provided by a component).

As mentioned in the documentation:

This lifecycle hook is triggered when a directive, pipe, or service is being destroyed.

For those curious about the topic of destruction, feel free to explore this question:

Answer 4

While I may not have all the details on every lifecycle hook, I do know that when it comes to destruction, ngOnDestroy is called for Injectable when its provider is destroyed (such as an Injectable provided by a component).

As mentioned in the documentation:

This lifecycle hook is triggered when a directive, pipe, or service is being destroyed.

For those curious about the topic of destruction, feel free to explore this question:

Answer 5

Answer №3

Contributing to the answer provided by @Sasxa,

You have the flexibility to utilize class in Injectables, where you can place your initial code within the constructor rather than using ngOnInit(). This approach functions effectively as well.

Answer 6

Contributing to the answer provided by @Sasxa,

You have the flexibility to utilize class in Injectables, where you can place your initial code within the constructor rather than using ngOnInit(). This approach functions effectively as well.

Answer 7

Answer №4

Important Note: This solution is specific to Angular components and directives, not services.

I encountered the same problem where lifecycle hooks like ngOnInit were not being triggered for my components, leading me to search for solutions.

The issue stemmed from using arrow function syntax (=>) in the following manner:

class MyComponent implements OnInit {
    // Avoid this: using arrow function
    public ngOnInit = () => {
        console.log("ngOnInit");
    }
}

It turns out that this approach does not work effectively in Angular 6. Instead, using traditional function syntax resolves the problem:

class MyComponent implements OnInit {
    public ngOnInit() {
        console.log("ngOnInit");
    }
}

Answer 8

Important Note: This solution is specific to Angular components and directives, not services.

I encountered the same problem where lifecycle hooks like ngOnInit were not being triggered for my components, leading me to search for solutions.

The issue stemmed from using arrow function syntax (=>) in the following manner:

class MyComponent implements OnInit {
    // Avoid this: using arrow function
    public ngOnInit = () => {
        console.log("ngOnInit");
    }
}

It turns out that this approach does not work effectively in Angular 6. Instead, using traditional function syntax resolves the problem:

class MyComponent implements OnInit {
    public ngOnInit() {
        console.log("ngOnInit");
    }
}

Answer 9

Answer №5

Instead of waiting for my dataService to be initialized, I decided to call the function inside the constructor and it ended up working perfectly.

Answer 10

Instead of waiting for my dataService to be initialized, I decided to call the function inside the constructor and it ended up working perfectly.

The ngOnInit function is not triggered upon instantiation of an Injectable class

Answer №1

Answer №2

Answer №3

Answer №4

Answer №5

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