The problem of course is that the file is not known to the onload event because of its delayed execution. One of the main difficulties is the accessing of file properties and contents at the same time, within the FileReader. FileReader includes four options for reading a file, asynchronously: Interestingly, the latter was not recognized by my Firefox 5 browser remember to perform browser support tests!
The method takes a starting byte as its first argument, ending byte as its second, and an option content type string as a third.
Reading Multiple Files and Properties Using a Closure Reading multiple files can be a little trickier, depending on how you do it. The server component would then be responsible for reconstructing the file content in the correct order. Blob - Allows for slicing a file into byte ranges.
Lucky for us, the File interface supports a slice method to support this use case. For instance, you can see it in the code above where I displayed the first line. Doing this makes it far easier to edit the script as it can be done in one place rather than editing the code within the script tags on each page that contains the script.
Thus, it is possible to monitor the progress of a read, catch errors, and determine when a load is complete. Your browser may not support the functionality in this article.
Reading files Now comes the fun part! We can modify the previous example slightly to include drag and drop support. Like the also asynchronous Ajax calls, the FileReader also has loading states that help to ascertain the progress of the read.
It would look like the example below. I employed the latter in the code snippet below because the readSingleFile function receives the event object as an argument.
Drop files here Note: This is also true of file reading. All the File APIs are supported. File - an individual file; provides readonly information such as name, file size, mimetype, and a reference to the file handle. Try dragging files onto the input field in the previous example.
The File object has some properties all on its own which have nothing to do with the FileReader, such as its name, type, size, and last modified date. Its associated onload event is where you should attach your processing logic. For instance, you could save it as write.