By utilizing ngOnInit() over a constructor, the @Input() property remains uninitialized

If this design is considered terrible, I am more than willing to make changes.

Within my index.html, in the body section, I have:

<month [year]="2016" [monthOfYear]="4">Loading...</month>

The contents of month.component.ts are as follows:

import { Component, Input, OnInit } from '@angular/core';
import { DayComponent } from '../day/day.component';
import * as Models from '../../../models/_models';

@Component({  
  selector: 'month',
  moduleId: module.id,
  templateUrl: 'month.component.html',
  styleUrls: ['month.component.css'],
  directives: [DayComponent]
})

export class MonthComponent {  
  name: string;
  days: Models.Day[];
  @Input('year') year: number;
  @Input('monthOfYear') monthOfYear: number;
  month: Models.Month;

  ngOnInit() {
    this.month = new Models.Month(this.year, this.monthOfYear);
    this.name = this.month.getMonthName();
    this.days = this.month.days;
  }
}

Despite ngOnInit() being called correctly, both year and monthOfYear are found to be undefined at that point. How can I ensure that the values are passed in during ngOnInit(), or is there a better approach to achieve this?

Answer №1

The answer to this problem may not have been easily understood from the tutorial or documentation.

Here is a straightforward solution:

<month year="2016" monthOfYear="4">Loading...</month>

When you see square brackets around attributes in a component, it means that those attributes are expected to be data bindings coming from the parent component. If you need to pass values from the parent component, use the following syntax:

<month [year]="year" [monthOfYear]="month">Loading...</month>

If you are assigning string literals in your case, there is no need for the square brackets. Additionally, declaring that your component implements OnInit does not seem to affect the execution of the code.

Answer №2

It seems like you are attempting to transfer some data from index.html to a Component (which essentially becomes the root component). However, it is important to note that Angular typically gets bootstrapped by the root component and may not be able to directly interact with index.html (the page hosting Angular).

In most cases, in index.html you will have a root component (such as AppComponent) which can then contain other components (like MonthComponent). The AppComponent is able to pass values to the MonthComponent.

I hope this clarifies things for you

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