详解JS+HTML5 FileReader的对象用法

<input name="file" id="uploadFile" />

var file = document.getElementById("uploadFile");
var bufferSize = 1024;
var pos = 0;
var onload = function(e) {
   console.log("Read", e.target.result);
   var img = document.createElement("img");
   img.src = e.target.result;
   img.width = 300;
   img.height = 300;
   document.body.appendChild(img);
};
var onerror = function() {}
var onprogress = function(e) {}
file.onchange = function() {
   if (file.files) file = file.files[0];
   while (pos < file.size) {
    var reader = new FileReader();
    reader.onload = onload;
    reader.onerror = onerror;
    /*reader.readAsText(file.slice(pos, bufferSize));
    pos += bufferSize; */
    reader.readAsDataURL(file);
    pos = file.size + 1;
   }
}