Question

How does xhr.upload.addEventListener(“error”, failed, false) differ from me having $success = move_uploaded_file($tmp_name, $name); if $(success) { echo "0" } else { echo "1" }? Is this unnecessary redundancy?

function uploadPHP() {
    var xhr = new XMLHttpRequest();

    xhr.upload.addEventListener("progress", updateProgress, false);
    xhr.upload.addEventListener("load", complete, false);
    xhr.upload.addEventListener("error", failed, false);
    xhr.upload.addEventListener("abort", cancelled, false);

    var foo = document.getElementById("uploadScreen");
    var form = document.getElementById("uploadForm");
    var percentComplete;
    var index;

    xhr.onreadystatechange = function () {
        if (xhr.readyState == 1){
        }
--

    function cancelled() {
        //cancel
    }
}

localhost file_server # cat php/upload.php

<?php
//
//require_once('PhpConsole.php');
//PhpConsole::start();
$tmp_name = $_FILES['file1']['tmp_name'];
$path = "/trunk";
$name = $path . DIRECTORY_SEPARATOR . $_FILES['file1']['name'];
$success = move_uploaded_file($tmp_name, $name);
if ($success) {
echo "0";
} else {
    echo "1";
}
?>

Answer 1

"error" occurs if your request doesn’t get through, for example if it times out.

Say you need to validate some data. If it is invalid, the "error" event won’t occur unless you throw an uncaught exception in your PHP. Instead, it will simply return some data that indicates the values were invalid, for example the string "0".

In your given example, it is entirely possible for the move_uploaded_file to fail, yet the error handler won’t trigger because technically the request completed without untoward incident. The only indication you will have of the action you wanted to take having failed will be the "0" response.