Help javascript

JavaScript
1 
const svgImage = document.getElementById("svgImage");
const svgContainer = document.getElementById("svgContainer");
var viewBox = {x:0,y:0,w:svgImage.clientWidth,h:svgImage.clientHeight};
svgImage.setAttribute('viewBox', `${viewBox.x} ${viewBox.y} ${viewBox.w} ${viewBox.h}`);
const svgSize = {w:svgImage.clientWidth,h:svgImage.clientHeight};
var isPanning = false;
var startPoint = {x:0,y:0};
var endPoint = {x:0,y:0};;
var scale = 1;
svgContainer.onmousewheel = function(e) {
   e.preventDefault();
   var w = viewBox.w;
   var h = viewBox.h;
   var mx = e.offsetX;//mouse x  
   var my = e.offsetY;    
   var dw = w*Math.sign(e.deltaY)*0.1;
   var dh = h*Math.sign(e.deltaY)*0.1;
   var dx = dw*mx/svgSize.w;
   var dy = dh*my/svgSize.h;
   viewBox = {x:viewBox.x+dx,y:viewBox.y+dy,w:viewBox.w-dw,h:viewBox.h-dh};
   scale = svgSize.w/viewBox.w;
   svgImage.setAttribute('viewBox', `${viewBox.x} ${viewBox.y} ${viewBox.w} ${viewBox.h}`);
}
svgContainer.onmousedown = function(e){
   isPanning = true;
   startPoint = {x:e.x,y:e.y};   
}
svgContainer.onmousemove = function(e){
   if (isPanning){
  endPoint = {x:e.x,y:e.y};
  var dx = (startPoint.x - endPoint.x)/scale;
  var dy = (startPoint.y - endPoint.y)/scale;
  var movedViewBox = {x:viewBox.x+dx,y:viewBox.y+dy,w:viewBox.w,h:viewBox.h};
  svgImage.setAttribute('viewBox', `${movedViewBox.x} ${movedViewBox.y} ${movedViewBox.w} ${movedViewBox.h}`);
   }
}
svgContainer.onmouseup = function(e){
   if (isPanning){ 
  endPoint = {x:e.x,y:e.y};
  var dx = (startPoint.x - endPoint.x)/scale;
  var dy = (startPoint.y - endPoint.y)/scale;
  viewBox = {x:viewBox.x+dx,y:viewBox.y+dy,w:viewBox.w,h:viewBox.h};
  svgImage.setAttribute('viewBox', `${viewBox.x} ${viewBox.y} ${viewBox.w} ${viewBox.h}`);
  isPanning = false;
   }
}
svgContainer.onmouseleave = function(e){
 isPanning = false;
}

Help me max zoom-in and max zoom-out