Display labels for points close to the mouse cursor. Could be used to display multiple tooltips, etc.
Uses k-nearest-neighbors algorithm from this block by llb4ll. Check the box to see the underlying quadtree (red points are the nearest points, orange are those that were searched but found to be not among the nearest).
https://cdnjs.cloudflare.com/ajax/libs/underscore.js/1.8.3/underscore-min.js
https://d3js.org/d3.v3.min.js