How do I calculate the angle between two points in HTML5?

I am attempting to create a 2d tile based game in Javascript, and I need to be able to calculate the angle between two points. I am using the atan2 function to find the angle between two points like so:

function getAngleDegrees(fromX, fromY, toX, toY, force360 = true) {
    let deltaX = toX - fromX;
    let deltaY = toY - fromY;
    let radians = Math.atan2(deltaY, deltaX);
    let degrees = (radians * 180) / Math.PI;
    if (force360) {
      while (degrees >= 360) degrees -= 360;
      while (degrees < 0) degrees += 360;
    }
    return degrees;
  }

However, this isn't providing me with the correct result. I have checked the code for logic or math errors and can't find any. No matter what points I input to this function the result will be off by many degrees.

I have created a JS fiddle to visualize the problem:

https://jsfiddle.net/fa6o7wdy/40/

If anyone knows how I can fix my angle function to provide the correct result please help!

Edit:

Here is a picture of the problem:

https://imgur.com/a/OXDCOux