1. 定义表单

2.调用图像流

var demo_h5_upload_ops = {    init:function(){        this.eventBind();    },    eventBind:function(){        var that = this;        $("#upload").change(function(){            var reader = new FileReader();            reader.onload = function (e) {                that.compress(this.result);            };            reader.readAsDataURL(this.files[0]);        });    },    compress : function (res) {        var that = this;        var img = new Image(),            maxH = 300;         img.onload = function () {            var cvs = document.createElement('canvas'),                ctx = cvs.getContext('2d');             if(img.height > maxH) {                img.width *= maxH / img.height;                img.height = maxH;            }            cvs.width = img.width;            cvs.height = img.height;             ctx.clearRect(0, 0, cvs.width, cvs.height);            ctx.drawImage(img, 0, 0, img.width, img.height);            var dataUrl = cvs.toDataURL('image/jpeg', 1);            $(".img_wrap").attr("src",dataUrl);            $(".img_wrap").show();            // 上传略            that.upload( dataUrl );        };         img.src = res;    },    upload:function( image_data ){        /*这里写上传方法,图片流是base64_encode的*/    }};  $(document).ready( function(){    demo_h5_upload_ops.init();} );