how do add touch pinch zoom in/out with jquery

Question

I am trying to add pinch zoom in and out to an uploaded image that is placed onto a canvas. I may have gone around it wrong to get it there but it works. I have everything with the mouse working including wheel zoom and touch to move it around but without zooming with pinch and I can not work out how to accomplish this. I need a little advice on where to begin.

I upload an image and save the data to an input field like so :

The html :

var canvas = document.getElementsByTagName('canvas')[0];
canvas.width = 250;
canvas.height = 170;

The JS to upload it is:

function readURL(input) {
    if (input.files && input.files[0]) {
        var reader = new FileReader();
        reader.onload = function(e) {       
            $('#new_img').val(e.target.result);
            load_img(e.target.result);          
        }
        reader.readAsDataURL(input.files[0]);       
    }
}

I then use this code to display it onto the canvas like :

var gkhead = new Image;
function load_img(){                    
    

var img_new = document.getElementById('new_img').value
        gkhead.src = img_new;                       
        var ctx = canvas.getContext('2d');
        trackTransforms(ctx);
                  
function redraw(){
      // Clear the entire canvas
      var p1 = ctx.transformedPoint(0,0);
      var p2 = ctx.transformedPoint(canvas.width,canvas.height);
      ctx.clearRect(p1.x,p1.y,p2.x-p1.x,p2.y-p1.y);

      ctx.save();
      ctx.setTransform(1,0,0,1,0,0);
      ctx.clearRect(0,0,canvas.width,canvas.height);
      ctx.restore();

      ctx.drawImage(gkhead,0,0);

    }
    redraw();

I have the mouse controls with :

var lastX=canvas.width/2, lastY=canvas.height/2;
  var dragStart,dragged;

  canvas.addEventListener('mousedown',function(evt){
      document.body.style.mozUserSelect = document.body.style.webkitUserSelect = document.body.style.userSelect = 'none';
      lastX = evt.offsetX || (evt.pageX - canvas.offsetLeft);
      lastY = evt.offsetY || (evt.pageY - canvas.offsetTop);
      dragStart = ctx.transformedPoint(lastX,lastY);
      dragged = false;
  },false);

  canvas.addEventListener('mousemove',function(evt){
      lastX = evt.offsetX || (evt.pageX - canvas.offsetLeft);
      lastY = evt.offsetY || (evt.pageY - canvas.offsetTop);
      dragged = true;
      if (dragStart){
        var pt = ctx.transformedPoint(lastX,lastY);
        ctx.translate(pt.x-dragStart.x,pt.y-dragStart.y);
        redraw();
            }
  },false);

  canvas.addEventListener('mouseup',function(evt){
      dragStart = null;
      if (!dragged) zoom(evt.shiftKey ? -1 : 1 );
  },false);

  var scaleFactor = 1.1;

  var zoom = function(clicks){
      var pt = ctx.transformedPoint(lastX,lastY);
      ctx.translate(pt.x,pt.y);
      var factor = Math.pow(scaleFactor,clicks);
      ctx.scale(factor,factor);
      ctx.translate(-pt.x,-pt.y);
      redraw();
  }

  var handleScroll = function(evt){
      var delta = evt.wheelDelta ? evt.wheelDelta/40 : evt.detail ? -evt.detail : 0;
      if (delta) zoom(delta);
      return evt.preventDefault() && false;
  };

  canvas.addEventListener('DOMMouseScroll',handleScroll,false);
  canvas.addEventListener('mousewheel',handleScroll,false);
};

function trackTransforms(ctx){
  var svg = document.createElementNS("http://www.w3.org/2000/svg",'svg');
  var xform = svg.createSVGMatrix();
  ctx.getTransform = function(){ return xform; };

  var savedTransforms = [];
  var save = ctx.save;
  ctx.save = function(){
      savedTransforms.push(xform.translate(0,0));
      return save.call(ctx);
  };

  var restore = ctx.restore;
  ctx.restore = function(){
    xform = savedTransforms.pop();
    return restore.call(ctx);
          };

  var scale = ctx.scale;
  ctx.scale = function(sx,sy){
    xform = xform.scaleNonUniform(sx,sy);
    return scale.call(ctx,sx,sy);
          };

  var rotate = ctx.rotate;
  ctx.rotate = function(radians){
      xform = xform.rotate(radians*180/Math.PI);
      return rotate.call(ctx,radians);
  };

  var translate = ctx.translate;
  ctx.translate = function(dx,dy){
      xform = xform.translate(dx,dy);
      return translate.call(ctx,dx,dy);
  };

  var transform = ctx.transform;
  ctx.transform = function(a,b,c,d,e,f){
      var m2 = svg.createSVGMatrix();
      m2.a=a; m2.b=b; m2.c=c; m2.d=d; m2.e=e; m2.f=f;
      xform = xform.multiply(m2);
      return transform.call(ctx,a,b,c,d,e,f);
  };

  var setTransform = ctx.setTransform;
  ctx.setTransform = function(a,b,c,d,e,f){
      xform.a = a;
      xform.b = b;
      xform.c = c;
      xform.d = d;
      xform.e = e;
      xform.f = f;
      return setTransform.call(ctx,a,b,c,d,e,f);
  };

  var pt  = svg.createSVGPoint();
  ctx.transformedPoint = function(x,y){
      pt.x=x; pt.y=y;
      return pt.matrixTransform(xform.inverse());
  } 
}

The touch code basically mimics the mouse movements I think like so :

 // Set up touch events for mobile, etc
    canvas.addEventListener("touchstart", function (e) {
            mousePos = getTouchPos(canvas, e);
      var touch = e.touches[0];
      var mouseEvent = new MouseEvent("mousedown", {
        clientX: touch.clientX,
        clientY: touch.clientY
      });
      canvas.dispatchEvent(mouseEvent);
    }, false);
    canvas.addEventListener("touchend", function (e) {
      var mouseEvent = new MouseEvent("mouseup", {});
      canvas.dispatchEvent(mouseEvent);
    }, false);
    canvas.addEventListener("touchmove", function (e) {
      var touch = e.touches[0];
      var mouseEvent = new MouseEvent("mousemove", {
        clientX: touch.clientX,
        clientY: touch.clientY
      });
      canvas.dispatchEvent(mouseEvent);
    }, false);
    
    // Get the position of a touch relative to the canvas
    function getTouchPos(canvasDom, touchEvent) {
      var rect = canvasDom.getBoundingClientRect();
      return {
        x: touchEvent.touches[0].clientX - rect.left,
        y: touchEvent.touches[0].clientY - rect.top
      };
    }

This all works as I explained and I have tried everything using different examples but getting nowhere. I have tried to adapt this example but it does not work and I can not debug on a mobile device?

https://codepen.io/AbramPlus/pen/mdymKom

Sorry if I have not explained or entered this correctly.