js实现下载图片方法

        function downLoad(){
             let image = new Image();
            // 解决跨域 Canvas 污染问题
            image.setAttribute("crossOrigin", "anonymous");
            image.onload = function () {
                let canvas = document.createElement("canvas");
                canvas.width = image.width;
                canvas.height = image.height;
                let context = canvas.getContext("2d");
                context.drawImage(image, 0, 0, image.width, image.height);
                let url = canvas.toDataURL("image/png"); //得到图片的base64编码数据
                let a = document.createElement("a"); // 生成一个a元素
                let event = new MouseEvent("click"); // 创建一个单击事件
                a.download = "头像"; // 设置图片名称
                a.href = url; // 将生成的URL设置为a.href属性
                a.dispatchEvent(event); // 触发a的单击事件
            };
            image.src = cnsUrl;
        }

file2base64

getPictureBase64(file) {
    return new Promise((resolve, reject) => {
	const reader = new FileReader();
	reader.readAsDataURL(file);
	reader.onload = () => resolve(reader.result);
	reader.onerror = error => reject(error);
	});
},

base642blob

base64ToBlob(data) {
   var arr = data.split(','),
    mime = arr[0].match(/:(.*?);/)[1],
    bstr = atob(arr[1]),
    n = bstr.length,
    u8arr = new Uint8Array(n);
    while (n--) {
        u8arr[n] = bstr.charCodeAt(n);
    }
    return new Blob([u8arr], { type: mime });
}