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function sliceBlob(blob, start, end, type) {

    type = type || blob.type;

    if (blob.mozSlice) {
        return blob.mozSlice(start, end, type);
    } else if (blob.webkitSlice) {
        return blob.webkitSlice(start, end type);
    } else {
        throw new Error("This doesn't work!");
    }
}

var builder = new BlobBuilder();
builder.append("Hello world!");
var blob = builder.getBlob("text/plain");

var blob = new Blob(["Hello world!"], { type: "text/plain" });

var URL = window.URL || window.webkitURL,
    imageUrl,
    image;

if (URL) {
    imageUrl = URL.createObjectURL(file);
    image = document.createElement("img");

    image.onload = function() {
        URL.revokeObjectURL(imageUrl);
    };

    image.src = imageUrl;
    document.body.appendChild(image);
}

var rangeData = {start: 0, end: 0, text: "" };
textarea.focus();

rangeData.start= el.selectionStart;
rangeData.end = el.selectionEnd;

rangeData.text = (rangeData.start != rangeData.end) ? el.value.substring(rangeData.start, rangeData.end): "";

oS = document.selection.createRange();

// 为了使 oR 与 oS 在同一等级上比较，请勿使用：oR = textarea.createTextRange()
oR = document.body.createTextRange();
oR.moveToElementText(textarea);

rangeData.text = oS.text;

    getBookmark: Retrieves a bookmark (opaque string) that can be used with moveToBookmark to return to the same range.

    moveToBookmark: Moves to a bookmark.

rangeData.bookmark = oS.getBookmark();

    compareEndPoints: Compares an end point of a TextRange object with an end point of another range.

    moveStart: Changes the start position of the range.

for (i = 0; oR.compareEndPoints('StartToStart', oS) < 0 && oS.moveStart("character", -1) !== 0; i ++) {}
rangeData.start = i;

for (i = 0; oR.compareEndPoints('StartToStart', oS) < 0 && oS.moveStart("character", -1) !== 0; i ++) {
    // Why? You can alert(textarea.value.length)
    if (textarea.value.charAt(i) == '\n') {
        i ++;
    }
}
rangeData.start = i;

rangeData.end = rangeData.text.length + rangeData.start;

/**
* getCursorPosition Method
*
* Created by Blank Zheng on 2010/11/12.
* Copyright (c) 2010 PlanABC.net. All rights reserved.
*
* The copyrights embodied in the content of this file are licensed under the BSD (revised) open source license.
*/
function getCursorPosition(textarea) {
    var rangeData = {text: "", start: 0, end: 0 };
        textarea.focus();
    if (textarea.setSelectionRange) { // W3C
        rangeData.start= textarea.selectionStart;
        rangeData.end = textarea.selectionEnd;
        rangeData.text = (rangeData.start != rangeData.end) ? textarea.value.substring(rangeData.start, rangeData.end): "";
    } else if (document.selection) { // IE
        var i,
            oS = document.selection.createRange(),
            // Don't: oR = textarea.createTextRange()
            oR = document.body.createTextRange();
        oR.moveToElementText(textarea);

        rangeData.text = oS.text;
        rangeData.bookmark = oS.getBookmark();

        // object.moveStart(sUnit [, iCount])
        // Return Value: Integer that returns the number of units moved.
        for (i = 0; oR.compareEndPoints('StartToStart', oS) < 0 && oS.moveStart("character", -1) !== 0; i ++) {
            // Why? You can alert(textarea.value.length)
            if (textarea.value.charAt(i) == '\n') {
                i ++;
            }
        }
        rangeData.start = i;
        rangeData.end = rangeData.text.length + rangeData.start;
    }

    return rangeData;
}

/**
* setCursorPosition Method
*
* Created by Blank Zheng on 2010/11/12.
* Copyright (c) 2010 PlanABC.net. All rights reserved.
*
* The copyrights embodied in the content of this file are licensed under the BSD (revised) open source license.
*/
function setCursorPosition(textarea, rangeData) {
    if(!rangeData) {
        alert("You must get cursor position first.")
    }
    if (textarea.setSelectionRange) { // W3C
        textarea.focus();
        textarea.setSelectionRange(rangeData.start, rangeData.end);
    } else if (textarea.createTextRange) { // IE
        var oR = textarea.createTextRange();
        // Fixbug :
        // In IE, if cursor position at the end of textarea, the setCursorPosition function don't work
        if(textarea.value.length === rangeData.start) {
            oR.collapse(false)
            oR.select();
        } else {
            oR.moveToBookmark(rangeData.bookmark);
            oR.select();
        }
    }
}

function Shape(name) {
  this.x = 0;
  this.y = 0;
  this.name = name;
  console.log('Shape constructor called');
}

Shape.prototype = {
  move: function(x, y) {
    this.x += x;
    this.y += y;
  },

  toString: function() {
    return 'name: ' + this.name + ', at x: ' + this.x + ', y:' + this.y;
  }
};

// Rectangle
function Rectangle(name) {
  this.name = name;
  console.log('Rectangle constructor called');
}

Rectangle.prototype = new Shape();

var rect = new Rectangle('Player 1');
rect.move(1, 1);
console.log(rect.toString());
console.log(rect instanceof Rectangle);

Shape constructor called
Rectangle constructor called
name: Player 1, at x: 1, y:1
true

Rectangle.prototype.move = function(x, y) {
  console.log('Super method called');
  Shape.prototype.move.apply(this, arguments);
};

loadstart – 当加载数据开始的时候，此事件通常都是使用在整个过程的最开始。
progress – 当数据读取的时候，可以获得数据读取进度。
error – 当数据加载失败的时候。
abort – 当数据加载被 abort() 方法取消的时候，（在 FileReader 和 XMLHttpRequest 都可用）。
load – 当所有数据都被成功加载的时候。
loadend – 当数据完成传输的时候，一般情况下，都是在出错，取消，或者成功加载后。所以其不区分成功与否。只要过程完成就好。

lengthComputable ─ true或者false，表示请求数据的大小是否已知。
loaded ─ 目前接收到的字节数。
total ─ 整个请求中期望传输的字节数。
注意：当lengthComputable为false时，total属性值为0。loadstart事件只会被激发一次。在loadstart之后，进度事件可能被激发0次或多次。

var reader = new FileReader(),
     progressNode = document.getElementById("my-progress");

reader.onprogress = function(event) {
    if (event.lengthComputable) {
        progressNode.max = event.total;
        progressNode.value = event.loaded;
    }
};

reader.onloadend = function(event) {
    var contents = event.target.result,
        error    = event.target.error;

    if (error != null) {
        console.error("File could not be read! Code " + error.code);
    } else {
        progressNode.max = 1;
        progressNode.value = 1;
        console.log("Contents: " + contents);
    }
};

reader.readAsText(file);

NotFoundError – 找不到文件。
SecurityError – 文件本身或者读取存在危险，一般情况下，如果读取此文件是危险的或者已经读取了太多次此文件，就会出现该错误。
NotReadableError – 文件存在，但是没有权限读取。
EncodingError – 编码错误，只要是作为 data URI 读取的时候，读取结果的长度超过了浏览器支持的最大长度。

FileError.NOT_FOUND_ERR -- NotFoundError.
FileError.SECURITY_ERR -- SecurityError.
FileError.NOT_READABLE_ERR -- NotReadableError.
FileError.ENCODING_ERR for -- EncodingError .
FileError.ABORT_ERR -- 当 abort() 方法调用的时候。

var reader = new FileReader();

reader.onloadend = function(event) {
    var contents = event.target.result,
        error    = event.target.error;

    if (error != null) {
        switch (error.code) {
            case error.ENCODING_ERR:
                console.error("Encoding error!");
                break;

            case error.NOT_FOUND_ERR:
                console.error("File not found!");
                break;

            case error.NOT_READABLE_ERR:
                console.error("File could not be read!");
                break;

            case error.SECURITY_ERR:
                console.error("Security issue with file!");
                break;

            default:
                console.error("I have no idea what's wrong!");
        }
    } else {
        progressNode.max = 1;
        progressNode.value = 1;
        console.log("Contents: " + contents);
    }
};

reader.readAsText(file);