I need to build a JavaScript function which takes two GeoJSON features as input: Feature A will be a Polygon or Circle; feature B will be a Point, Polygon, Circle or Ellipse.
The function should return, as quickly and efficiently as possible, whether B "touches" A in any way (whether they overlap, whether one is contained within the other, e.g.)
Extreme precision is not important (i.e. I don't care about issues arising from, say, the curvature of the Earth); I also don't need to know any details about how the two features touch one another, just a boolean TRUE or FALSE as to whether or not they do.
If there's a good solution that requires a module, that's perfectly fine -- the only thing that's important is that the actual function is as fast as reasonably possible. E.g. it looks like Turf can do this, but would require executing a few separate functions (intersect, contains, etc.) some of which are overly heavy.
Fortunately there's a JavaScript port of JTS (Java Topology Suite) - library of spatial predicates and functions for processing geometry conforming to the Simple Features Specification (a standard from the Open Geospatial Consortium)
Its name is JSTS (GeoJSON support included)
https://github.com/bjornharrtell/jsts
Intersection of A and B
var intersection = a.intersection(b)
Difference of A and B
var difference = a.difference(b)
Union of A and B
var union = a.union(b)
Check the test suite for all the use cases including Point in Polygon tests https://github.com/bjornharrtell/jsts/tree/master/test
Also, visual example integrated with Openlayers (with source code): https://openlayers.org/en/master/examples/jsts.html
EDIT 1:
In case you want just one function something like this will do:
var intersection = (a.intersection(b) !== null) ? true : false;