代码如下：

function onInitFs(fs) {
  fs.root.getFile('log.txt', {create: true}, function(fileEntry) {  

   fileEntry.createWriter(function(fileWriter) {  
   fileWriter.onwriteend = function(e) { console.log('Write completed.'); };  

   fileWriter.onerror = function(e) { console.log('Write failed: ' + e.toString()); };  
     window.BlobBuilder = window.BlobBuilder || window.WebKitBlobBuilder;
//第41行
var bb = new BlobBuilder();

   bb.append('Lorem Ipsum'); 
   fileWriter.write(bb.getBlob('text/plain'));  }, errorHandler);  }, errorHandler);  }  
      window.requestFileSystem = window.requestFileSystem || window.webkitRequestFileSystem;
  window.requestFileSystem(window.TEMPORARY, 1024*1024, onInitFs, errorHandler); 

浏览器报错

Uncaught TypeError: undefined is not a function  第41行