Javascript – How to validate that 2 folders on the same level cannot have the same name in a recursive Angular form array

My answer will be fully working with the Reactive forms.

To summarize your requirements and the work on:

1. Not allow duplicate names in the same directory.

   1.1. Implement the custom validator function duplicateFolderName based on the provided parentDirectory. We have 2 scenarios:

   1.1.1. The first case is the folder with the first level which itself is the root. We access the folderHierarchy form array (control.parent.parent) to get the same-level object(s).

   1.1.2. The second case is the folder that has the parent. We provide the parentDirectory which contains the subfolders form array and through it to get the same-level object(s).

   1.2. For the FolderHierarchyComponent, you need to implement the parentDirectory @Input decorator to pass the parent form to the component. Note that for first level folder shouldn’t provide the value to [parentDirectory].

2. Perform validation(s) only when pressing Enter key.

   2.1. Angular supports the event that triggers the validation only such as blur, submit, and change (default). For this scenario, add the validateOn: 'blur' to the name control. Next, set the (keyup.enter)="folderName.blur()" to the name control to blur (lose focus) the control when pressing Enter key.

form.component.html

<p>folder form. type in form name and press enter</p>
<form [formGroup]="myForm">
  <div formArrayName="folderHierarchy">
    <label for="folderHierarchy">create folder </label>
    <div>
      <div>
        <button
          type="button"
          class="btn btn-custom rounded-corners btn-circle mb-2"
          (click)="addFolder()"
          [disabled]="!folderHierarchy.valid"
        >
          Add
        </button>
        <span class="pl-1"> new folder</span>
      </div>
      <div>
        <div *ngIf="!folderHierarchy.valid" class="folder-hierarchy-error">
          invalid folder hierarchy
        </div>
        <div class="folderContainer">
          <div>
            <div
              *ngFor="let folder of folderHierarchy.controls; let i = index"
              [formGroupName]="i"
            >
              <folder-hierarchy
                (remove)="removeFolder(i)"
                [folder]="getForm(folder)"
                [index]="i"
              >
              </folder-hierarchy>
            </div>
          </div>
        </div>
      </div>
    </div>
  </div>
</form>

form.component.ts

import { duplicateFolderName } from '../validators/duplicate-folder-name.validator';

export class FormComponent implements OnInit {
  myForm!: FormGroup;
  isHierarchyVisible: boolean = false;

  constructor(private formBuilder: FormBuilder) {}

  ngOnInit() {
    this.myForm = this.formBuilder.group({
      folderHierarchy: this.formBuilder.array([]),
    });
    if (this.folderHierarchy.length === 0) this.isHierarchyVisible = false;
  }

  removeFolder(index: number): void {
    this.folderHierarchy.removeAt(index);
    if (this.folderHierarchy.length === 0) this.isHierarchyVisible = false;
  }

  addFolder(): void {
    this.folderHierarchy.push(
      this.formBuilder.group({
        name: [
          null,
          {
            validators: [
              Validators.required,
              duplicateFolderName(),
            ],
            updateOn: 'blur',
          },
        ],
        subFolders: this.formBuilder.array([]),
        level: 0,
      })
    );
    this.isHierarchyVisible = true;
  }

  getForm(control: AbstractControl): FormGroup {
    return control as FormGroup;
  }

  get folderHierarchy(): FormArray {
    return this.myForm.get('folderHierarchy') as FormArray;
  }
}

folder-hierarchy.component.html

<div *ngIf="folder" #folderRow class="folder-row" [formGroup]="folder">
  <div class="folder-header">
    <div class="folder-name-container">
      <label for="folderName" class="folder-name-label">Name:</label>
      <input
        #folderName
        id="folderName"
        [ngClass]="nameControl.errors ? 'invalid-input' : ''"
        class="folder-name-input"
        placeholder="Folder Name"
        type="text"
        maxlength="50"
        autocomplete="off"
        name="name"
        formControlName="name"
        (keyup.enter)="folderName.blur()"
      />
    </div>

    <button
      type="button"
      class="btn-remove-folder"
      (click)="removeFolder(folder)"
    >
      Remove
    </button>

    <button
      type="button"
      class="btn-add-subfolder"
      [disabled]="disableAdd(folder)"
      (click)="addSubFolder(folder)"
    >
      Add Subfolder
    </button>
  </div>

  <div
    *ngIf="folder && folder.value.subFolders.length > 0"
    class="subfolder-container"
  >
    <div
      *ngFor="
        let subFolder of getSubFoldersControls(folder);
        let i = index
      "
      class="subfolder-item"
    >
      <folder-hierarchy
        (remove)="removeSubFolder(folder, i)"
        [folder]="subFolder"
        [parentDirectory]="folder"
      >
      </folder-hierarchy>
    </div>
  </div>

  <div
    *ngIf="nameControl.errors && nameControl.errors.required"
    class="folder-hierarchy-error"
  >
    Name is required.
  </div>

  <div
    *ngIf="nameControl.errors && nameControl.errors.duplicateName"
    class="folder-hierarchy-error"
  >
    Name already exists
  </div>
</div>

folder-hierarchy.component.ts

import { duplicateFolderName } from '../validators/duplicate-folder-name.validator';

@Component({
  selector: 'folder-hierarchy',
  templateUrl: './folder-hierarchy.component.html',
  styleUrls: ['./folder-hierarchy.component.css'],
})
export class FolderHierarchyComponent implements OnInit {
  constructor(private formBuilder: FormBuilder) {}
  @Output() remove = new EventEmitter();
  @Input() folder!: FormGroup;
  @Input() index!: number;
  @Input() parentDirectory?: FormGroup;

  ngOnInit() {}

  addSubFolder(folder: FormGroup): void {
    (folder.get('subFolders') as FormArray).push(
      this.formBuilder.group({
        name: [
          null,
          {
            validators: [
              Validators.required,
              duplicateFolderName(this.parentDirectory),
            ],
            updateOn: 'blur',
          },
        ],
        subFolders: this.formBuilder.array([]),
        level: folder.value.level + 1,
      })
    );
  }

  getControls(folder: FormGroup): FormArray {
    return folder.get('subFolders') as FormArray;
  }

  getSubFoldersControls(folder: FormGroup): FormGroup[] {
    return (folder.get('subFolders') as FormArray).controls as FormGroup[];
  }

  removeSubFolder(folder: FormGroup, index: number): void {
    (folder.get('subFolders') as FormArray).removeAt(index);
  }

  removeFolder(folder: { value: { subFolders: string | any[] } }): void {
    this.remove.emit(folder);
  }

  disableAdd(folder: { invalid: any }): void {
    return this.folder.invalid || folder.invalid;
  }

  get nameControl() {
    return this.folder.get('name') as FormControl;
  }
}

validators/duplicate-folder-name.validator.ts

import {
  AbstractControl,
  FormArray,
  FormGroup,
  ValidatorFn,
} from '@angular/forms';

export const duplicateFolderName = (
  parentDirectory?: FormGroup
): ValidatorFn => {
  return (control: AbstractControl): { [key: string]: any } | null => {
    if (!control.value) return null;

    let folderNamesInSameDirectory: string[] = parentDirectory
      ? (parentDirectory.get('subFolders').value as any[]).map((x) => x.name)
      : (control.parent.parent.value as any[]).map((x) => x.name);

    console.log(folderNamesInSameDirectory);

    if (folderNamesInSameDirectory.indexOf(control.value) > -1)
      return {
        duplicateName: true,
      };

    return null;
  };
};

Demo @ StackBlitz