无法读取未定义的属性“chrome”

Question

是什么原因造成的，如何避免？我无法捕捉到异常。
第一次chooseEntry被取消createWriter有时会抛出异常，我可以捕捉到这个：

Error in response to fileSystem.chooseEntry: TypeError: Cannot call method 'createWriter' of undefined

然后当我再次尝试调用 chooseEntry 时，会抛出此异常：

try{
    chrome.fileSystem.chooseEntry({ type:'saveFile',suggestedName:$("#mydiv").text()+".jpg",accepts:[{ extensions:['jpg'] }] },function(fileEntry){
        try{
            fileEntry.createWriter(function(writer) {
                writer.onerror = errorHandler;
                writer.onwriteend = function(e) { console.log('write complete'); };
                writer.write(data); //data is a blob
            });
        }catch(err){ console.log("error",err.message); }
    });
}catch(err){ console.log("error",err.message); }

> Error in response to fileSystem.chooseEntry: TypeError: Cannot read property 'chrome' of undefined

Answer 1

为了避免第一次异常检查未定义的文件条目，

       try{
          if(fileEntry) { 
              fileEntry.createWriter(function(writer) {
                writer.onerror = errorHandler;
                writer.onwriteend = function(e) { console.log('write complete'); };
                writer.write(data); //data is a blob
             });
           }
        }catch(err){ console.log("error",err.message); }