vue3 下载图片实现方法，亲测有效

        //图片编码 
        const getUrlBase64 = (url) => {
            return new Promise((resolve) => {
                let canvas = document.createElement("canvas");
                let ctx = canvas.getContext("2d");
                let img = new Image();
                img.crossOrigin = "Anonymous"; //允许跨域
                img.src = url;
                img.onload = function () {
                    canvas.height = 300;
                    canvas.width = 300;
                    ctx.drawImage(img, 0, 0, 300, 300);
                    let dataURL = canvas.toDataURL("image/png");
                    canvas = null;
                    resolve(dataURL);
                };
            });
        };

        // click事件调用方法
        const download_qr_code = (item) => {
            getUrlBase64(item).then((base64) => {
                let link = document.createElement("a");
                link.href = base64;
                link.download = "qrCode.png";
                link.click();
            });
        };