js 图片压缩上传（base64位）以及上传类型分类

一、input file上传类型

1.指明只需要图片

<input type="file" accept='image/*'>

2.指明需要多张图片

<input type="file" multiple accept='image/*'>

3.指明调用摄像头获取图片

<input type="file" capture='camera' accept='image/*'>

4.调用摄像头并获取多张图片（摄像头只能单张获取，multiple无效）

<!-- multiple 无效 -->
<input type="file" multiple capture='camera' accept='image/*'>

二、图片压缩上传

（1）移动端IOS上传的某些图片预览时发生了旋转？

　　你会发现手机截图，网络图片都不会有旋转问题，只有手机拍摄的才有，这就跟拍摄时的角度有问题了，所以我们通过 exif.js 获取角度（Orientation）的值，所获值分别需要旋转的角度如下：

旋转角度	参数值
0°	1
顺时针90°	6
逆时针90°	8
180°	3

<!DOCTYPE html>
<html>
    <head>
        <meta charset="UTF-8">
        <title></title>
        <meta name="viewport" content="width=device-width,initial-scale=1,minimum-scale=1,maximum-scale=1,user-scalable=no" />
        <script src="js/jquery-1.11.3.min.js"></script>
        <script src="js/exif.js"></script>
        <style>
            #preview{
                width:100px;
                height:110px;
            }
        </style>
    </head>
    <body>
        <input type="file" id="files" >
        <img src="blank.gif" id="preview">
        
<script>
    
var ipt = document.getElementById('files'),
    img = document.getElementById('preview'),
    Orientation = null;
ipt.onchange = function () {
    var file = ipt.files[0],
        reader = new FileReader(),
        image = new Image();
        
    if(file){
        EXIF.getData(file, function() {  
            Orientation = EXIF.getTag(this, 'Orientation');
            console.log(Orientation);
        });
        reader.onload = function (ev) {
            image.src = ev.target.result;
            image.onload = function () {
                var imgWidth = this.width,
                    imgHeight = this.height;
                // 控制上传图片的宽高
                if(imgWidth > imgHeight && imgWidth > 600){
                    imgWidth = 600;
                    imgHeight = Math.ceil(600 * this.height / this.width);
                }else if(imgWidth < imgHeight && imgHeight > 600){
                    imgWidth = Math.ceil(600 * this.width / this.height);
                    imgHeight = 600;
                }
                var canvas = document.createElement("canvas"),
                ctx = canvas.getContext('2d');
                canvas.width = imgWidth;
                canvas.height = imgHeight;
                if(Orientation && Orientation != 1){
                    switch(Orientation){
                        case 6:     // 旋转90度
                            canvas.width = imgHeight;    
                            canvas.height = imgWidth;    
                            ctx.rotate(Math.PI / 2);
                            ctx.drawImage(this, 0, -imgHeight, imgWidth, imgHeight);
                            break;
                        case 3:     // 旋转180度
                            ctx.rotate(Math.PI);    
                            ctx.drawImage(this, -imgWidth, -imgHeight, imgWidth, imgHeight);
                            break;
                        case 8:     // 旋转-90度
                            canvas.width = imgHeight;    
                            canvas.height = imgWidth;    
                            ctx.rotate(3 * Math.PI / 2);    
                            ctx.drawImage(this, -imgWidth, 0, imgWidth, imgHeight);
                            break;
                    }
                }else{
                    ctx.drawImage(this, 0, 0, imgWidth, imgHeight);
                }
                var newImageData = canvas.toDataURL("image/jpeg", 0.6);
                $("img").attr("src", newImageData.replace("data:base64", "data:image/jpeg;base64"));
            }
        }
        reader.readAsDataURL(file);
    }
}
</script>
    </body>
</html>