记录一下：前端压缩图片

 //这里处理点击上传事件
    $('#clipbg-btn').click(function () {
        var cas = $('#cropper-img').cropper('getCroppedCanvas');
        var base64 = cas.toDataURL('image/jpeg');
        $("#finalImg").prop("src", base64); // 显示图片
        $(".header-img").addClass('no-bg');
        // var data = encodeURIComponent(base64); //如果需要URI编码，则使用这个
        closecropper()
        $(".header-img img").attr('src', base64)
        $(".header-img img").removeClass('default');
        $(".btn upload").text('上传中···')
        $(".upload").attr('disabled', 'disabled');
        mui.showLoading("正在上传.....","div");
        var bili = 1.5;　　// 压缩比例
        console.log("压缩前base64-length：" + base64.length);
        suofang(base64, bili, addPicture);
    })

    var suofang = function(base64, bili, callback) {
        console.log("执行缩放程序,bili=" + bili);
        //处理缩放，转格式
        var _img = new Image();
        _img.src = base64;
        _img.onload = function() {
            var _canvas = document.createElement("canvas");
            var w = this.width / bili;
            var h = this.height / bili;
            _canvas.setAttribute("width", w);
            _canvas.setAttribute("height", h);
            _canvas.getContext("2d").drawImage(this, 0, 0, w, h);
            var base64 = _canvas.toDataURL("image/jpeg");
            _canvas.toBlob(function(blob) {
                console.log(blob.size);

                if(blob.size > 1024*1024){
                    suofang(base64, bili, callback);
                }else{
                    callback(blob, base64);
                }
            }, "image/jpeg");
        }
    }

    function addPicture(blob,base64) {
        // console.log("base64:  " + base64)
        if (base64.indexOf("image/png") > -1){
            base64 = base64.replace('png', 'jpeg');
        };
         $.ajax({
            type: "post",
            url: "/app/face/updateUserFaceInfo",
            data: {
                "base64": base64
            },
            success: function(r) {
                console.log(JSON.stringify(r))
                $(".upload").removeAttr('disabled');
                mui.hideLoading();
             
                /* 上传后操作的动作放这里 */
            }
        });
    }