// 将base64转blob
    dataURLtoBlob(dataurl: any) {
        var arr = dataurl.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 });
    },
    //将blob转换为file
    blobToFile(theBlob: any, fileName: any) {
        theBlob.lastModifiedDate = new Date();
        theBlob.name = fileName;
        return theBlob;
    },
/**
     * 压缩图片到指定大小
     */
    compressImage(base64: any, w: any, format: any = 'image/png', callback: any) {
        var newImage = new Image();
        var quality = 0.6;    //压缩系数0-1之间
        newImage.src = base64;
        newImage.setAttribute("crossOrigin", 'Anonymous');  //url为外域时需要
        var imgWidth, imgHeight;
        newImage.onload = function () {
            imgWidth = 160;
            imgHeight = 90;
            var canvas = document.createElement("canvas");
            let ctx:any = canvas.getContext("2d");
            if (Math.max(imgWidth, imgHeight) > w) {
                if (imgWidth > imgHeight) {
                    canvas.width = w;
                    canvas.height = w * imgHeight / imgWidth;
                } else {
                    canvas.height = w;
                    canvas.width = w * imgWidth / imgHeight;
                }
            } else {
                canvas.width = imgWidth;
                canvas.height = imgHeight;
                quality = 0.6;
            }
            ctx.clearRect(0, 0, canvas.width, canvas.height);
            ctx.drawImage(this, 0, 0, canvas.width, canvas.height);
            var base64 = canvas.toDataURL(format, quality); //压缩语句
            // 如想确保图片压缩到自己想要的尺寸,如要求在50-150kb之间，请加以下语句，quality初始值根据情况自定
            while (base64.length / 1024 > 150) {
                quality -= 0.01;
                base64 = canvas.toDataURL(format, quality);
            }
            // 防止最后一次压缩低于最低尺寸，只要quality递减合理，无需考虑
            // while (base64.length / 1024 < 50) {
            //  quality += 0.001;
            //  base64 = canvas.toDataURL("image/jpeg", quality);
            // }
            callback(base64);//必须通过回调函数返回，否则无法及时拿到该值，return拿不到
        }
    }

调用
1、base64Data：传获取到的base64字符串
2、newBase64Data：返回压缩后的base64
3、image/png：是base64开头的那一节

console.log('base64Data', base64Data.length); // 原长度
compressImage(base64Data, 150, 'image/png', (newBase64Data: any) => {
        console.log('newBase64Data', newBase64Data.length); // 压缩后的长度
        const blob = dataURLtoBlob(newBase64Data);
         const file = blobToFile(blob, 'image.png');
         const formData = new FormData();
         formData.append("file", file);
         console.log('formData', formData);
});