Passing parameters to an Angular 2 component

When it comes to passing a string parameter to my component, I need the flexibility to adjust the parameters of services based on the passed value. Here's how I handle it: In my index.html, I simply call my component and pass the required parameter.

<top [mode]="tree">Loading...</top>

To enable this functionality in my component, I first import Input from angular2/core.

import {Input, Component, OnInit} from 'angular2/core';

Then, within my component's class, I declare an input property for the mode.

@Input() mode: string;

However, when I attempt to access the passed parameter ('tree') using console.log(), I find that it's coming up as undefined.

console.log(this, this.mode);

https://i.stack.imgur.com/mHNPN.jpg

If you're interested in seeing the complete code snippet for the component file:

import {Http, HTTP_PROVIDERS} from 'angular2/http';
import {Input, Component, OnInit} from 'angular2/core';
import {ParticipantService} from '../services/participant.service';
import {orderBy} from '../pipes/orderby.pipe';

@Component({
    selector: 'top',
    templateUrl: 'dev/templates/top.html',
    pipes: [orderBy],
    providers: [HTTP_PROVIDERS, ParticipantService]
})
export class AppTopComponent implements OnInit {

    constructor (private _participantService: ParticipantService) {}

    errorMessage: string;
    participants: any[];
    @Input() mode: string;

    ngOnInit() {
        console.log(this, this.mode);
        this.getParticipants('top3');
        var self = this;
        setInterval(function() {
            self.getParticipants('top3');
        }, 3000);
    }

    getParticipants(public mode: string) {
        this._participantService.getParticipants(mode)
            .then(
                participants => this.participants = participants,
                error => this.errorMessage = <any>error
            );
    }

}

Answer №1

When utilizing `[...]`, the value you input must be an expression that is able to be evaluated.

Therefore, the variable tree needs to refer to a string that exists in the parent component.

If you wish to utilize the string tree, follow this format:

<top mode="tree">Loading...</top>

Please note that these parameters are not suitable for the root component. Refer to the following question for further information:

  • Angular 2 input parameters on root directive

Answer №2

To overcome the restriction Thierry mentioned, one possible solution is to utilize

constructor(private _userService: UserService, 
    elRef:ElementRef) {
  this.type=elRef.nativeElement.getAttribute('type');
}

Answer №3

Ensure that you wait for the template to be connected to the DOM before making any changes. To achieve this, it is recommended to utilize AfterViewInit in your implementation.

    export class TopAppComponent implements AfterViewInit{

    public ngAfterViewInit() {
        console.log(this, this.mode);
        this.fetchTopParticipants('top3');
        var self = this;
        setInterval(function() {
            self.fetchTopParticipants('top3');
        }, 3000);
    }
   }

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