FileReader load a file

by Graham Fairweather

HTML

<input type="file" id="files" name="file" />
<button id="cancel">Cancel read</button>
<div id="progress_bar">
    <div class="percent">0%</div>
</div>
<div>Base64 encoded result</div>
<textarea id="display"></textarea>

CSS

#progress_bar {
    margin: 10px 0;
    padding: 3px;
    border: 1px solid #000;
    font-size: 14px;
    clear: both;
    opacity: 0;
    -moz-transition: opacity 1s linear;
    -o-transition: opacity 1s linear;
    -webkit-transition: opacity 1s linear;
}
#progress_bar.loading {
    opacity: 1.0;
}
#progress_bar .percent {
    background-color: #99ccff;
    height: auto;
    width: 0;
}
#display {
    width: 500px;
    height: 150px;
}

JavaScript

/*jslint sub: true, maxerr: 50, indent: 4, browser: true */
/*global */

(function () {
    "use strict";

    var reader,
    progress = document.querySelector(".percent"),
        display = document.getElementById("display"),
        iFiles = document.getElementById("files"),
        bCancel = document.getElementById("cancel"),
        dropZone = document.getElementById("drop_zone"),
        filebox = document.getElementById("filebox"),
        list = document.getElementById("list");

    function abortRead() {
        if (reader) {
            reader.abort();
        }
    }

    function errorHandler(evt) {
        switch (evt.target.error.code) {
            case evt.target.error.NOT_FOUND_ERR:
                alert("File Not Found!");
                break;
            case evt.target.error.NOT_READABLE_ERR:
                alert("File is not readable");
                break;
            case evt.target.error.ABORT_ERR:
                break; // noop
            default:
                alert("An error occurred reading this file.");
        };
    }

    function updateProgress(evt) {
        // evt is an ProgressEvent.
        if (evt.lengthComputable) {
            var percentLoaded = Math.round((evt.loaded / evt.total) * 100);
            // Increase the progress bar length.
            if (percentLoaded < 100) {
                progress.style.width = percentLoaded + "%";
                progress.textContent = percentLoaded + "%";
            }
        }
    }

    function handleFileSelect(evt) {
        // Reset progress indicator on new file selection.
        progress.style.width = "0%";
        progress.textContent = "0%";

        reader = new FileReader();
        reader.onerror = errorHandler;
        reader.onprogress = updateProgress;
        reader.onabort = function (e) {
            alert('File read cancelled');
        };

        reader.onloadstart = function (e) {
            document.getElementById('progress_bar').className =...