How do grammar checking extensions operate on Google Docs?

Other Questions Google docs
1

Developing Chrome extensions for grammar checking in Google Docs is challenging since documents render using canvas. How do tools overlay interface elements without traditional DOM APIs? Example below:

function fetchOverlayElements() {
  const canvasElem = document.querySelector('.doc-canvas');
  if (canvasElem) {
    // Implement custom overlay positioning logic
    console.log('Overlay activated.');
  }
}
2

From my experience working with Chrome extensions and Google Docs, integrating grammar checking tools presents unique hurdles due to the reliance on canvas-based rendering. I observed that developers often create an additional overlay layer that uses CSS and JavaScript to track the document’s viewport, syncing positions precisely with the displayed text. This involves utilizing MutationObservers and custom coordinate mapping to connect the canvas rendering with interactive elements. Although it is a non-standard method compared to working directly with conventional DOM, the end result offers a smooth user experience.

3

Working on similar projects, I found that the challenge lies in bridging the gap between canvas rendering and HTML-based user interfaces. In my experience, an effective solution is to create a dedicated overlay that mirrors the text positions by calculating offsets and scales dynamically. This overlay is updated in real-time with event listeners and custom logic that responds to viewport changes. Although this adds complexity to the development, careful tuning of the synchronization mechanism ensures that users receive accurate grammar feedback without noticeable delays.