The File API

We may not be able to save files directly to the user's filesystem, but we can access files using HTML5's File API. The File API allows you to get information about, and load the contents of, files that the user selects. The user can select files using an input element with a type of file. The process for loading a file works in the following way:

  1. The user selects one or more files using a <input type="file"> element.
  2. We get the list of files from the input element's files property. The list is a FileList object containing File objects.
  3. You can enumerate over the file list and access the files just like you would an array.

    The File object contains three fields.

    • name: This is the filename. It doesn't include path information.
    • size: This is the size of the file in bytes.
    • type: This is the MIME type, if it can be determined.
  4. Use a FileReader object to read the file's data. The file is loaded asynchronously. After the file has been read, it will call the onload event handler. FileReader has a number of methods for reading files that take a File object and return the file contents.
    • readAsArrayBuffer(): This method reads the file contents into an ArrayBuffer object.
    • readAsBinaryString(): This method reads the file contents into a string as binary data.
    • readAsText(): This method reads the file contents into a string as text.
    • readAsDataURL(): This method reads the file contents into a data URL string. You can use this as the URL for loading an image.
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