Calculate whether a difference in angle is clockwise or anticlockwise.

angles.js

function isClockwise(from, to) {
  let diff = normalize(from) - normalize(to);
  return normalize(diff) > 180;
}

// Returns angle normalized to between [0, 360).
function normalize(angle) {
  while (angle < 0) {
    angle += 360;
  }
  while (angle >= 360) {
    angle -= 360;
  }
  return angle;
}

let tests = [
  // Clockwise
  [0, 90, true],
  [90, 180, true],
  [180, 270, true],
  [270, 0, true],

  // Counter-clockwise
  [0, 270, false],
  [270, 180, false],
  [180, 90, false],
  [90, 0, false],

  // 179 degree angles
  [179, 0, false],
  [181, 0, true],

  // Arbitrary ones
  [180, 0, false], // arbitrary
  [0, 0, false],   // arbitrary

  // Input invalid
  [720, 0, false],
  [0, 720, false],
];

let failures = tests.reduce(function(failedTests, t) {
  let actual = isClockwise(t[0], t[1]);
  let expected = t[2];
  if (actual != expected) {
    console.log("Failed: isClockWise("+t[0]+", "+t[1]+")="+actual+", wanted="+expected);
    return failedTests + 1;
  }
  return failedTests;
}, 0);

if (failures == 0) {
  console.log("OK");
}