Vue实现剪切板图片压缩

const that = this;
    document.body.addEventListener('paste', function (event) {
        that.$fullScreenLoading.show("读取图片中");
        // 获取当前输入框内的文字
        const oldText = that.$refs.msgInputContainer.textContent;
        // 读取图片
        let items = event.clipboardData && event.clipboardData.items;
        let file = null;
        if (items && items.length) {
            // 检索剪切板items
            for (let i = 0; i < items.length; i++) {
                if (items[i].type.indexOf('image') !== -1) {
                    file = items[i].getAsFile();
                    break;
                }
            }
        }
        // 预览图片
        const reader = new FileReader();
        reader.onload = function(event) {
            // 图片内容
            const imgContent = event.target.result;
            // 创建img标签
            let img = document.createElement('img');//创建一个img
            // 获取当前base64图片信息，计算当前图片宽高以及压缩比例
            let imgObj = new Image();
            let imgWidth = "";
            let imgHeight = "";
            let scale = 1;
            imgObj.src = imgContent;
            imgObj.onload = function() {
                // 计算img宽高
                if(this.width<400){
                    imgWidth = this.width;
                    imgHeight = this.height;
                }else{
                    // 输入框图片显示缩小10倍
                    imgWidth = this.width/10;
                    imgHeight = this.height/10;
                    // 图片宽度大于1920，图片压缩5倍
                    if(this.width>1920){
                        // 真实比例缩小5倍
                        scale = 5;
                    }
                }
                // 设置可编辑div中图片宽高
                img.width = imgWidth;
                img.height = imgHeight;
                // 压缩图片，渲染页面
                that.compressPic(imgContent,scale,function (newBlob,newBase) {
                    // 删除可编辑div中的图片名称
                    that.$refs.msgInputContainer.textContent = oldText;
                    img.src = newBase; //设置链接
                    // 图片渲染
                    that.$refs.msgInputContainer.append(img);
                    that.$fullScreenLoading.hide();
                });
            };
        };
        reader.readAsDataURL(file);
    });

// 参数: base64地址,压缩比例，回调函数(返回压缩后图片的blob和base64)
    compressPic:function(base64, scale, callback){
        const that = this;
        let _img = new Image();
        _img.src = base64;
        _img.onload = function() {
            let _canvas = document.createElement("canvas");
            let w = this.width / scale;
            let h = this.height / scale;
            _canvas.setAttribute("width", w);
            _canvas.setAttribute("height", h);
            _canvas.getContext("2d").drawImage(this, 0, 0, w, h);
            let base64 = _canvas.toDataURL("image/jpeg");
            // 当canvas对象的原型中没有toBlob方法的时候，手动添加该方法
            if (!HTMLCanvasElement.prototype.toBlob) {
                Object.defineProperty(HTMLCanvasElement.prototype, 'toBlob', {
                    value: function (callback, type, quality) {
                        let binStr = atob(this.toDataURL(type, quality).split(',')[1]),
                            len = binStr.length,
                            arr = newUint8Array(len);
                        for (let i = 0; i < len; i++) {
                            arr[i] = binStr.charCodeAt(i);
                        }
                        callback(new Blob([arr], {type: type || 'image/png'}));
                    }
                });
            }else{
                _canvas.toBlob(function(blob) {
                    if(blob.size > 1024*1024){
                        that.compressPic(base64, scale, callback);
                    }else{
                        callback(blob, base64);
                    }
                }, "image/jpeg");
            }
        }
    }