How to Autofocus Next Input Field in Angular's Directive

IntroductionIn web development, handling user input is a common task. When it comes to keyboard input, it's important to consider scenarios where users type rapidly or continuously. Uncontrolled input events can lead to unnecessary function calls or excessive network requests. To address this, developers often implement a technique called "autofocusing" to optimize the handling of keyboard input. In this blog post, we'll explore how to autofocus the next input field using Angular directive.The HTML StructureLet's start by examining the HTML structure of our example code:

html
<app-child2></app-child2>1 input in component directive<br />
<input type="text" [autofocusNext]="true" maxlength="10" />2 input autofocusNext
<br />
<input type="text" />3 input without autofocusNext <br />
<app-chidl1></app-chidl1>4 input in component directive<br />
<input type="text" [autofocusNext]="true" maxlength="15" />5 input
autofocusNext<br />
<input type="text" />6 input without autofocusNext <br />
<input type="text" [autofocusNext]="true" maxlength="8" />7 input
autofocusNext<br />

In this code snippet, we have several input elements with and without the autofocusNext directive. The autofocusNext directive is used to autofocus the next input field when the current input field reaches its maximum length.Autofocusing the Next Input FieldNow, let's dive into the TypeScript code that handles the autofocus functionality:

typescript
import { Directive, ElementRef, HostListener, Input } from '@angular/core';

@Directive({
  selector: '[autofocusNext]',
})
export class AutofocusNextDirective {
  @Input() autofocusNext: boolean = true;

  constructor(private el: ElementRef) {}

  @HostListener('input', ['$event.target'])
  onInput(target: HTMLInputElement): void {
    if (!this.autofocusNext) {
      return;
    }

    const maxLength = target.maxLength || Infinity;
    const currentLength = target.value.length;

    if (currentLength >= maxLength) {
      const nextInput = this.getNextEligibleInput(target);

      if (nextInput) {
        nextInput.focus();
      }
    }
  }

  private getNextEligibleInput(
    currentInput: HTMLInputElement
  ): HTMLInputElement {
    const allInputs = this.getAllEligibleInputs();
    const currentIndex = allInputs.indexOf(currentInput);

    return allInputs[currentIndex + 1] as HTMLInputElement;
  }

  private getAllEligibleInputs(): HTMLInputElement[] {
    const allInputs = document.querySelectorAll(
      'input[ng-reflect-autofocus-next]'
    );
    return Array.from(allInputs) as HTMLInputElement[];
  }
}

In this code, we have a AutofocusNextDirective class that implements the autofocus functionality. This directive listens to the input event and checks if the autofocusNext property is set to true. If it is, the directive checks if the current input field has reached its maximum length. If it has, the directive finds the next eligible input field using the getNextEligibleInput method and sets the focus to it.The getNextEligibleInput method finds the next eligible input field by getting all the input fields with the autofocusNext directive and finding the index of the current input field. It then returns the next input field in the array.The getAllEligibleInputs method gets all the input fields with the autofocusNext directive using a query selector.

https://stackblitz.com/edit/my-angular-boilerplate-gzataw?file=src%2Fapp%2Fautofocus-next.directive.ts



Conclusion

Autofocusing the next input field is a valuable technique for optimizing the handling of user input in web applications. By implementing a directive that listens to the input event and checks the autofocusNext property, we can control the focus of input fields and improve performance. In this blog post, we explored a simple example of how to autofocus the next input field using Angular. By understanding and applying this technique, you can enhance the user experience and create more efficient web applications.