What Text Area Popovers Taught Me About Browser APIs

My recent foray into building WYSIWYG editors and popovers yielded some fascinating insights into browser APIs. Maternity leave provided the perfect opportunity for deep dives into technical challenges without the pressure of deadlines.

My current focus is contributing to "codename goose," an open-source AI agent with a Rust backend and an Electron-based chat interface. I submitted a pull request to integrate a WYSIWYG editor, opting for a custom solution over existing packages to minimize bundle size. However, the maintainers suggested a popover toolbar to address space concerns.

Creating this floating toolbar proved unexpectedly challenging. My goals were straightforward:

• Display a popover toolbar upon text selection.
• Precisely position it above the selection.
• Account for word wrapping across multiple lines.
• Maintain accurate positioning during scrolling.

Text areas presented unique complexities. Unlike standard HTML elements, where content manipulation and precise positioning are readily available, text areas expose only raw text and basic selection APIs. The browser handles the rendering internally.

To illustrate, consider this analogy:

• Standard HTML elements: A house where you can rearrange furniture, add items, and measure distances.
• Text areas: A window into a room you can't enter. You can see and modify the contents (add/remove text), but direct manipulation is impossible. The browser manages the internal workings via native OS text editing.

Popover Challenges Beyond Text Areas

The Popover API

Modern browsers offer a built-in Popover API for creating pop-up elements. Here's an example:

Limitations

Despite its cross-browser compatibility and ease of use, the Popover API has limitations:

• It only functions with button elements due to the popovertarget attribute restriction.
• Popover positioning relies on CSS relative to the target element.
• Critically, it's incompatible with text areas.

Thanks to Mark Techson, who introduced me to the Popover API through Una Kravets' conference talk, "Less Cruft, More Power: Leverage the Power of the Web Platform."

The Selection API

To position the popover based on user text selection, I needed:

• The selected text's position.
• Event listeners for selection and deselection.

Colby Fayock's blog post, "How to Share Selected Text in React with the Selection API," introduced me to the Selection API (accessible via window.getSelection()). This API returns a Selection object detailing the selected text.

getRangeAt(0)

The getRangeAt(0) method within the Selection object provides the selection's start and end offsets:

• startOffset: The selection's beginning index.
• endOffset: The selection's ending index (after the last selected character).

For example, in "Hello, World! Welcome.", selecting "World" yields startOffset = 7 and endOffset = 12.

Note: getRangeAt(0) accesses the first selection. Browsers like Firefox allow multiple selections (Ctrl-click), but accessing indexes beyond 0 in single-selection browsers results in errors.

getBoundingClientRect()

getRangeAt(0) provides access to getBoundingClientRect(), which returns a bounding box with the selected text's top, right, bottom, left coordinates, width, and height. This allows for precise popover placement above the selection, as demonstrated:

However, this approach is limited within text areas.

The Mirrored Div

The "mirrored div" technique, discovered through discussions with Claude, offers a workaround. An invisible div overlays the text area, mirroring its content and styling. User interactions occur within this div, providing full Selection API access while maintaining a standard text area appearance.

Jhey Thompkins' blog post, "HOW TO: Where's the text cursor?", and the getComputedStyle() method (which returns an element's computed CSS styles) were instrumental in precisely matching the text area's appearance in the overlay div.

However, this mirroring isn't perfect:

• Text wrapping may differ between the div and text area.
• Browser-specific spacing and font rendering can cause positional discrepancies.

Why Not Use an NPM Package?

Many packages work well with standard DOM elements, but struggle with text areas due to the same fundamental limitations: restricted access to internal rendering and positioning.

Conclusion

Despite advancements in rich text interaction, working with text areas remains surprisingly complex. Exploring these browser APIs was a rewarding experience. Future APIs may simplify tasks like selection-based popovers. If you've encountered alternative solutions, I'd appreciate hearing about them.

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