JavaScript: Find the angle between two points

angle-between-points.js

var p1 = {
	x: 20,
	y: 20
};

var p2 = {
	x: 40,
	y: 40
};

// angle in radians
var angleRadians = Math.atan2(p2.y - p1.y, p2.x - p1.x);

// angle in degrees
var angleDeg = Math.atan2(p2.y - p1.y, p2.x - p1.x) * 180 / Math.PI;

Would love a version of this that has 0 degrees at due north if anyone knows how to do that...

@drewbaker

There are probably more elegant solutions to this but I achieved the desired behavior in p5.js using its map function which maps a value from one number range to another with the following syntax map(value, min1, max1, min2, max2)

My updated getAngle() function looks like this:

function getAngle(x1, y1, x2, y2){
  var a = Math.atan2(y2 - y1, x2 - x1) * (180 / Math.PI) + 90;
  a = (a < 0) ? map(a, -90, 0, 270, 360) : a;
  return a;
}

The map() function (always handy to have around) works like this under the hood:

function map(value, min1, max1, min2, max2) {
  return min2 + (max2 - min2) * ((value - min1) / (max1 - min1));
}

Thanks @timjuedemann but I actually wrote a function for this eventually that allows you to change where zero is, and even calculates distance from cursor to the element too.

Check it out here: https://github.com/funkhaus/fuxt/blob/master/utils/angleDistanceToCursor.js