Using ngOnChanges to Trigger Whether to Show an Overlay Depending on Input Changes

As a TypeScript developer, you may often come across situations where you need to show or hide an overlay depending on changes in the input values. In Angular, you can achieve this functionality using the ngOnChanges lifecycle hook.

The ngOnChanges hook is called whenever there is a change in the input properties of a component. By utilizing this hook, you can easily determine whether to display an overlay based on the changes in the input values.

Let’s explore a few solutions to implement this functionality:

Solution 1: Using ngOnChanges with Simple Input Property

If you have a single input property, you can directly use ngOnChanges to check for changes and show or hide the overlay accordingly. Here’s an example:

    import { Component, Input, OnChanges, SimpleChanges } from '@angular/core';

    @Component({
      selector: 'app-overlay',
      template: `
        

          
        
      `
    })
    export class OverlayComponent implements OnChanges {
      @Input() inputValue: string;
      showOverlay: boolean = false;

      ngOnChanges(changes: SimpleChanges) {
        if (changes.inputValue && !changes.inputValue.firstChange) {
          this.showOverlay = true;
        } else {
          this.showOverlay = false;
        }
      }
    }
  

In the above code snippet, we have an OverlayComponent with an input property called inputValue. Inside the ngOnChanges hook, we check if the inputValue has changed and it’s not the initial change. If both conditions are met, we set the showOverlay property to true, which will display the overlay.

Solution 2: Using ngOnChanges with Multiple Input Properties

If you have multiple input properties and want to trigger the overlay based on any of them, you can modify the ngOnChanges implementation as follows:

    import { Component, Input, OnChanges, SimpleChanges } from '@angular/core';

    @Component({
      selector: 'app-overlay',
      template: `
        

          
        
      `
    })
    export class OverlayComponent implements OnChanges {
      @Input() input1: string;
      @Input() input2: number;
      showOverlay: boolean = false;

      ngOnChanges(changes: SimpleChanges) {
        if (changes.input1 || changes.input2) {
          this.showOverlay = true;
        } else {
          this.showOverlay = false;
        }
      }
    }
  

In this solution, we check if any of the input properties (input1 or input2) have changed. If any change is detected, we set the showOverlay property to true, triggering the display of the overlay.

By utilizing the ngOnChanges hook, you can easily control the visibility of an overlay based on input changes. This allows you to provide a more dynamic and interactive user experience in your TypeScript applications.

That’s it! You now have two solutions to trigger the display of an overlay based on input changes using the ngOnChanges hook in Angular.

Happy coding!