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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);

function Animal() {
}

console.log(Animal.prototype);

function Animal() {
}

Animal.prototype.type = 'Unknown';
Animal.prototype.weight = 0;
Animal.prototype.weightUnits = 'kg';

Animal.prototype.toString = function() {
  return this.type + ', ' + this.weight + this.weightUnits;
};

var molly = new Animal();
molly.type = 'Dog';
molly.weight = 28;

console.log(molly.toString());

function Animal() {
}

Animal.prototype = {
  type: 'Unknown',
  weight: 0,
  weightUnits: 'kg',

  toString: function() {
    return this.type + ', ' + this.weight + this.weightUnits;
  }
};

var molly = new Animal(), harley = new Animal();

molly.type = 'Dog';
molly.weight = 28;

harley.type = 'Dog';
harley.weight = 38;
harley.name = 'Harley';

console.log(molly);// { type: 'Dog', weight: 28 }
console.log(harley);// { type: 'Dog', weight: 38, name: 'Harley' }

var molly = new Animal();

Animal.prototype.weightUnits = 'oz';

molly.type = 'Dog';
molly.weight = 28;

console.log(molly.toString());//'Dog, 28oz'

String.prototype.match = function() {
  return true;
};

console.log('alex'.match(/1234/));

var molly = new Animal(), harley;

molly.type = 'Dog';
molly.weight = 28;

Animal.prototype = {
  toString: function() { // 改写原生的 toString 方法。
    return '...';
  }
};

harley = new Animal;
harley.type = 'Dog';
harley.weight = 38;

console.log(molly.toString());// Dog, 28kg
console.log(harley.toString());// ...

readAsText() – 返回文本数据(text/plain)。
readAsBinaryString() – 返回此文件被编码的二进制数据 (已弃用– 使用 readAsArrayBuffer() 代替)。
readAsArrayBuffer() – 返回此文件的一个ArrayBuffer（二进制数据缓冲）（适合二进制数据，例如图像文件)数据。
readAsDataURL() – 返回此文件的 <a href="http://en.wikipedia.org/wiki/Data_URI_scheme" title="Data URI scheme" target="_blank">data URL</a>

var reader = new FileReader();
reader.onload = function(event) {
    var contents = event.target.result;
    console.log("File contents: " + contents);
};//文件读取完成

reader.onerror = function(event) {
    console.error("File could not be read! Code " + event.target.error.code);
};//文件读取错误

reader.readAsText(file);//以文本方式读取

var reader = new FileReader();
reader.onload = function(event) {//成功读取
    var dataUri = event.target.result,//数据内容
        img     = document.createElement("img");//创建一个 img 对象

    img.src = dataUri; //设置 img 对象的 src 属性值为 dataUri
    document.body.appendChild(img);//将 img 插入到 body 中
};

reader.onerror = function(event) {
    console.error("File could not be read! Code " + event.target.error.code);
};//读取文件错误是发生

reader.readAsDataURL(file);// 以 data url 方式读取数据

var reader = new FileReader();
reader.onload = function(event) {
    var dataUri = event.target.result,
        context = document.getElementById("mycanvas").getContext("2d"),
    img     = new Image();
    img.onload = function() {// 等待图像文件被加载完
        canvas.drawImage(img, 100, 100);
    };
    img.src = dataUri;
};

reader.onerror = function(event) {
    console.error("File could not be read! Code " + event.target.error.code);
};

<input type="file">

name – 文件名
size – 文件大小
type – 文件的 MIME 类型。

<input type="file" id="your-files" multiple>
<script>
var control = document.getElementById("your-files");
control.addEventListener("change", function(event) {
    // 当 control 改变的时候
    var i = 0,
        files = control.files,
        len = files.length;
    for (; i < len; i++) {
        console.log("Filename: " + files[i].name);
        console.log("Type: " + files[i].type);
        console.log("Size: " + files[i].size + " bytes");
    }
}, false);
</script>

<div id="your-files">&lt;/div>
<script>
var target = document.getElementById("your-files");

target.addEventListener("dragover", function(event) {
    event.preventDefault();
}, false);

target.addEventListener("drop", function(event) {

    // 阻止浏览器默认动作
    event.preventDefault();

    var i = 0,
        files = event.dataTransfer.files,
        len = files.length;

    for (; i < len; i++) {
        console.log("Filename: " + files[i].name);
        console.log("Type: " + files[i].type);
        console.log("Size: " + files[i].size + " bytes");
    }

}, false);
</script>

var form = new FormData();
form.append("name", "Nicholas");

// 创建一个有多个数据的表单
var form = new FormData();
form.append("name", "Nicholas");
form.append("photo", control.files[0]);

// 通过 XHR 传送，没有传送 header!
var xhr = new XMLHttpRequest();
xhr.onload = function() {
    console.log("Upload complete.");
};
xhr.open("post", "/entrypoint", true);
xhr.send(form);

$_POST["name"];
$_POST["photo"];