Intersection detection between two line segments in 2d space.

import segseg from 'segseg'
/*
                (0, 5)
                   │
  (-10, 0) ────────+───────  (10, 0)
                   │
                (0, -5)
*/
const isect = [ NaN, NaN ] // the output vector where collision point is stored
//                       seg 1                   seg 2
//                ┌───────────────────┐   ┌─────────────────┐
if (segseg(isect, [ -10, 0 ], [ 10, 0 ],  [ 0, 5 ], [ 0, -5 ]))
    console.log('intersected!', isect.join(','))  // output:   intersected! 0,0

You can also specify an epsilon value, which sets the maximum distance for a segment to be considered on another segment. By default this is 0, but there are some use cases where you might want to adjust this. For example, if you are working on a pixel based rendering, and want any segments within 1 of each other to be considered intersecting, since it's rendering will make it visually appear to be on the segment:

const EPSILON = 1
//                   seg 1               seg 2
//            ┌────────────────┐   ┌────────────────┐
segseg(isect, [ 1, 1 ], [ 5, 3 ],  [ 3, 3 ], [ 5, 6 ], ESPILON)  // returns true

This is a pure es module, and requires node v12+ to run. However if you're using a popular bundler such as rollup, webpack, etc. This should be compatible with most frontend setups too.

This code was ported from Mukesh Prasad's example implementation which was included in graphics gems 2.

Internally the code uses a point-segment check for some edge cases, from https://gist.github.com/mattdesl/47412d930dcd8cd765c871a65532ffac