add support for external modals; fixes #1571 (#1575)

docs/pages/resources/changelog.md

@@ -14,6 +14,7 @@ New versions of Shoelace are released as-needed and generally occur when a criti
 
 ## Next
 
+- Added the `modal` property to `<sl-dialog>` and `<sl-drawer>` to support third-party modals [#1571]
 - Fixed a bug in the autoloader causing it to register non-Shoelace elements [#1563]
 - Fixed a bug in `<sl-switch>` that resulted in improper spacing between the label and the required asterisk [#1540]
 - Removed error when a missing popup anchor is provided [#1548]

src/components/dialog/dialog.component.ts

@@ -60,6 +60,10 @@ import type { CSSResultGroup } from 'lit';
  * @animation dialog.denyClose - The animation to use when a request to close the dialog is denied.
  * @animation dialog.overlay.show - The animation to use when showing the dialog's overlay.
  * @animation dialog.overlay.hide - The animation to use when hiding the dialog's overlay.
+ *
+ * @property modal - Exposes the internal modal utility that controls focus trapping. To temporarily disable focus
+ *   trapping and allow third-party modals spawned from an active Shoelace modal, call `modal.activateExternal()` when
+ *   the third-party modal opens. Upon closing, call `modal.deactivateExternal()` to restore Shoelace's focus trapping.
  */
 export default class SlDialog extends ShoelaceElement {
   static styles: CSSResultGroup = styles;
@@ -69,8 +73,8 @@ export default class SlDialog extends ShoelaceElement {
 
   private readonly hasSlotController = new HasSlotController(this, 'footer');
   private readonly localize = new LocalizeController(this);
-  private modal = new Modal(this);
   private originalTrigger: HTMLElement | null;
+  public modal = new Modal(this);
 
   @query('.dialog') dialog: HTMLElement;
   @query('.dialog__panel') panel: HTMLElement;

src/components/drawer/drawer.component.ts

@@ -68,15 +68,19 @@ import type { CSSResultGroup } from 'lit';
  * @animation drawer.denyClose - The animation to use when a request to close the drawer is denied.
  * @animation drawer.overlay.show - The animation to use when showing the drawer's overlay.
  * @animation drawer.overlay.hide - The animation to use when hiding the drawer's overlay.
+ *
+ * @property modal - Exposes the internal modal utility that controls focus trapping. To temporarily disable focus
+ *   trapping and allow third-party modals spawned from an active Shoelace modal, call `modal.activateExternal()` when
+ *   the third-party modal opens. Upon closing, call `modal.deactivateExternal()` to restore Shoelace's focus trapping.
  */
 export default class SlDrawer extends ShoelaceElement {
   static styles: CSSResultGroup = styles;
   static dependencies = { 'sl-icon-button': SlIconButton };
 
   private readonly hasSlotController = new HasSlotController(this, 'footer');
   private readonly localize = new LocalizeController(this);
-  private modal = new Modal(this);
   private originalTrigger: HTMLElement | null;
+  public modal = new Modal(this);
 
   @query('.drawer') drawer: HTMLElement;
   @query('.drawer__panel') panel: HTMLElement;

src/internal/modal.ts

@@ -5,20 +5,23 @@ let activeModals: HTMLElement[] = [];
 
 export default class Modal {
   element: HTMLElement;
+  isExternalActivated: boolean;
   tabDirection: 'forward' | 'backward' = 'forward';
   currentFocus: HTMLElement | null;
 
   constructor(element: HTMLElement) {
     this.element = element;
   }
 
+  /** Activates focus trapping. */
   activate() {
     activeModals.push(this.element);
     document.addEventListener('focusin', this.handleFocusIn);
     document.addEventListener('keydown', this.handleKeyDown);
     document.addEventListener('keyup', this.handleKeyUp);
   }
 
+  /** Deactivates focus trapping. */
   deactivate() {
     activeModals = activeModals.filter(modal => modal !== this.element);
     this.currentFocus = null;
@@ -27,13 +30,24 @@ export default class Modal {
     document.removeEventListener('keyup', this.handleKeyUp);
   }
 
+  /** Determines if this modal element is currently active or not. */
   isActive() {
     // The "active" modal is always the most recent one shown
     return activeModals[activeModals.length - 1] === this.element;
   }
 
-  checkFocus() {
-    if (this.isActive()) {
+  /** Activates external modal behavior and temporarily disables focus trapping. */
+  activateExternal() {
+    this.isExternalActivated = true;
+  }
+
+  /** Deactivates external modal behavior and re-enables focus trapping. */
+  deactivateExternal() {
+    this.isExternalActivated = false;
+  }
+
+  private checkFocus() {
+    if (this.isActive() && !this.isExternalActivated) {
       const tabbableElements = getTabbableElements(this.element);
       if (!this.element.matches(':focus-within')) {
         const start = tabbableElements[0];
@@ -56,11 +70,9 @@ export default class Modal {
     return getTabbableElements(this.element).findIndex(el => el === this.currentFocus);
   }
 
-  /**
-   * Checks if the `startElement` is already focused. This is important if the modal already
-   * has an existing focus prior to the first tab key.
-   */
-  startElementAlreadyFocused(startElement: HTMLElement) {
+  // Checks if the `startElement` is already focused. This is important if the modal already has an existing focus prior
+  // to the first tab key.
+  private startElementAlreadyFocused(startElement: HTMLElement) {
     for (const activeElement of activeElements()) {
       if (startElement === activeElement) {
         return true;
@@ -70,8 +82,8 @@ export default class Modal {
     return false;
   }
 
-  handleKeyDown = (event: KeyboardEvent) => {
-    if (event.key !== 'Tab') return;
+  private handleKeyDown = (event: KeyboardEvent) => {
+    if (event.key !== 'Tab' || this.isExternalActivated) return;
 
     if (event.shiftKey) {
       this.tabDirection = 'backward';