Javascript: get the angle by which the element is rotated

get_rotate.js

function getRotationAngle(target) 
{
  const obj = window.getComputedStyle(target, null);
  const matrix = obj.getPropertyValue('-webkit-transform') || 
    obj.getPropertyValue('-moz-transform') ||
    obj.getPropertyValue('-ms-transform') ||
    obj.getPropertyValue('-o-transform') ||
    obj.getPropertyValue('transform');

  let angle = 0; 

  if (matrix !== 'none') 
  {
    const values = matrix.split('(')[1].split(')')[0].split(',');
    const a = values[0];
    const b = values[1];
    angle = Math.round(Math.atan2(b, a) * (180/Math.PI));
  } 

  return (angle < 0) ? angle +=360 : angle;
}


// example
console.log(getRotationAngle(document.getElementById('i-am-rotated')));

Thank You!

Can we do this in canvas ?
If yes, what are the values for X and Y ?
If no, how I can to know the values of X and Y in canvas ?