代码如下

var cvs = document.getElementById("cvs");var ctx = cvs.getContext("2d");var exportImage = document.getElementById("export");var img = document.getElementById("img");var hat = "hat6";var canvasFabric;var hatInstance;var screenWidth = window.screen.width < 500 ? window.screen.width : 300;function viewer() {  var file = document.getElementById("upload").files[0];  console.log(file);  var reader = new FileReader;  if (file) {    reader.readAsDataURL(file);    reader.onload = function(e) {      img.src = reader.result;      img.onload = function() {        img2Cvs(img)      }    }  } else {    img.src = ""  }}function img2Cvs(img) {  cvs.width = img.width;  cvs.height = img.height;  cvs.style.display = "block";  canvasFabric = new fabric.Canvas("cvs", {    width: screenWidth,    height: screenWidth,    backgroundImage: new fabric.Image(img, {      scaleX: screenWidth / img.width,      scaleY: screenWidth / img.height    })  });  changeHat();  document.getElementById("uploadContainer").style.display = "none";  document.getElementById("uploadText").style.display = "none";  document.getElementById("upload").style.display = "none";  document.getElementById("change").style.display = "block";  document.getElementById("exportBtn").style.display = "block";  document.getElementById("tip").style.opacity = 1}function changeHat() {  document.getElementById(hat).style.display = "none";  var hats = document.getElementsByClassName("hide");  hat = "hat" + (+hat.replace("hat", "") + 1) % hats.length;  var hatImage = document.getElementById(hat);  hatImage.style.display = "block";  if (hatInstance) {    canvasFabric.remove(hatInstance)  }  hatInstance = new fabric.Image(hatImage, {    top: 40,    left: screenWidth / 3,    scaleX: 100 / hatImage.width,    scaleY: 100 / hatImage.height,    cornerColor: "#0b3a42",    cornerStrokeColor: "#fff",    cornerStyle: "circle",    transparentCorners: false,    rotatingPointOffset: 30  });  hatInstance.setControlVisible("bl", false);  hatInstance.setControlVisible("tr", false);  hatInstance.setControlVisible("tl", false);  hatInstance.setControlVisible("mr", false);  hatInstance.setControlVisible("mt", false);  canvasFabric.add(hatInstance)}function exportFunc() {  document.getElementsByClassName("canvas-container")[0].style.display = "none";  document.getElementById("exportBtn").style.display = "none";  document.getElementById("tip").innerHTML = "长按图片保存或分享";  document.getElementById("change").style.display = "none";  cvs.style.display = "none";  exportImage.style.display = "block";  exportImage.src = canvasFabric.toDataURL({    width: screenWidth,    height: screenWidth  })}