HTML FileReader - html

Question

function fileSelected() {
// get selected file element
var files = document.getElementById('files[]').files;
for (var i = 0; i < files.length; i++) //for multiple files
{
(function (file) {
var fileObj = {
Size: bytesToSize(file.size),
Type: file.type,
Name: file.name,
Data: null
};
var reader = new window.FileReader();
reader.onload = function (e) {
fileObj.Data = e.target.result;
};
// read selected file as DataURL
reader.readAsDataURL(file);
//Create Item
CreateFileUploadItem(fileObj);
})(files[i]);
}
}
function CreateFileUploadItem (item) {
console.log(item);
$('<li>', {
"class": item.Type,
"data-file": item.Data,
"html": item.Name + ' ' + item.Size
}).appendTo($('#filesForUpload'));
}
So when console.log(item) gets run in the CreateFileUploadItem function it shows the item.Data. YET it won't add it to the data-file of the LI. Why is that?

Answer 1

The call to readAsDataURL is asynchronous. Thus, the function call is likely returning prior to the onload function being called. So, the value of fileObj.Data is still null when you are attempting to use it in CreateFileUploadItem.
To fix it, you should move the call to CreateFileUploadItem into your onload function. As for the console logging the proper value, you can't rely on that being synchronous either. I think using a breakpoint during debugging at that line instead will likely show the true null value.