Proposal: close() Method for the sidePanel API

proposals/sidepanel-close-api.md

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+# New close() Method for the sidePanel API
+
+**Summary**
+
+Proposal to introduce a programmatic close method for the side panel API.
+
+**Document Metadata**
+
+**Author:** [hharshas](https://github.com/hharshas)
+
+**Sponsoring Browser:** Chromium
+
+**Contributors:** [hharshas](https://github.com/hharshas) ([Summer Of
+Code](https://summerofcode.withgoogle.com/)), mentor: oliverdunk, solomonkinard
+
+**Created:** 2025-05-27
+
+**Related Issues:** [#521](https://github.com/w3c/webextensions/issues/521),
+[#chromium](https://issues.chromium.org/issues/403765214)
+
+## Motivation
+
+### Objective
+
+What does this API enable?
+- `sidePanel.close()` method will allow the sidebar to close programmatically.
+
+Why do we need it?
+- Currently, extensions cannot directly close their own side panel from the
+  background script, developers have to:
+  1. Send a message from a background script to the side panel.
+  2. Call `window.close()` from the side panel window on message delivery.
+
+This event aims to give developers an easier control.
+
+#### Use Cases
+
+Programmatic Control:
+- An extension could automatically close the panel after completing an action or
+  when certain conditions are met. For example, an extension that helps users fill
+  out a form could close the side panel automatically once the form is submitted.
+  This ensures the side panel only stays open while it’s needed,
+  streamlining the user experience.
+
+### Known Consumers
+
+[The Chromium bug](https://issues.chromium.org/issues/403765214) has a significant
+amount of developer interest and the discussions on the issue shows the same.
+
+## Specification
+
+### Schema
+
+```typescript
+namespace sidePanel {
+  dictionary CloseOptions {
+    // The window in which to close the side panel.
+    long? windowId;
+
+    // The tab for which to close the side panel. If specified,
+    // only closes tab-specific side panels.
+    long? tabId;
+
+    // At least one of these must be provided, otherwise rejects with an error.
+  };
+
+  interface Functions {
+    // Closes the extension's side panel.
+    // `options`: Specifies the context in which to close the side panel.
+    // `callback`: Called when the side panel has been closed.
+    static void close(
+      CloseOptions options,
+      optional VoidCallback callback);
+  };
+};
+```
+
+### Return value
+
+- Type: Promise<void>
+
+- Resolves when the panel has been closed. If the panel is
+  already closed, still resolves successfully.
+
+### Behavior
+
+- The operation will only close side panels that belong to the
+  calling extension.
+- If the panel is already closed or does not exist in the given
+  context, the method does nothing.
+- If neither `windowId` nor `tabId` is provided, rejects with an error.
+- If `windowId` or `tabId` is invalid, rejects with an error.
+- If both `windowId` and `tabId` are provided, the method will verify
+  that the tab belongs to the specified window. If not, it rejects with an error.
+
+### New Permissions
+N/A
+
+### Manifest File Changes
+N/A
+
+## Security and Privacy
+
+### Exposed Sensitive Data
+
+This API does not expose any sensitive data.
+
+### Abuse Mitigations
+
+The API is limited to closing only the extension's own side panel.
+
+### Additional Security Considerations
+
+N/A
+
+## Alternatives
+
+### Existing Workarounds
+
+* Message passing between background and panel contexts.
+* Calling `window.close()` from the panel context.
+
+### Open Web API
+
+Not applicable to the open web as it only complements the existing `open()`
+functionality.
+
+## Implementation Notes
+
+N/A
+
+## Future Work
+
+This implementation will align with
+[#779](https://github.com/w3c/webextensions/pull/779), to ensure proper event
+handling on panel closure (Open for discussion).