js實現canvas保存圖片為png格式並下載到本地

1. canvas 保存圖片

2. 下載到本地

   function base64Img2Blob(code){
                   var parts = code.split(';base64,');
                   var contentType = parts[0].split(':')[1];
                   var raw = window.atob(parts[1]);
                   var rawLength = raw.length;
   
                   var uInt8Array = new Uint8Array(rawLength);
   
                   for (var i = 0; i < rawLength; ++i) {
                     uInt8Array[i] = raw.charCodeAt(i);
                   }
   
                   return new Blob([uInt8Array], {type: contentType}); 
               }
               function downloadFile(fileName, content){
                  
                   var aLink = document.createElement('a');
                   var blob = base64Img2Blob(content); //new Blob([content]);
                 
                   var evt = document.createEvent("HTMLEvents");
                   evt.initEvent("click", false, false);//initEvent 不加后兩個參數在FF下會報錯
                   aLink.download = fileName;
                   aLink.href = URL.createObjectURL(blob);
            
                   aLink.dispatchEvent(evt);
               }           
   downloadFile('ship.png', canvas.toDataURL("image/png"));