export async function compressBase64(base64) {return new Promise((resolve, reject) => {const w = 500;//第一个参数就是原来的字符串，第二个是宽度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 = this.width;imgHeight = this.height;var canvas = document.createElement("canvas");var ctx = 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("image/jpeg", 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("image/jpeg", 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);}resolve(base64); //必须通过回调函数返回，否则无法及时拿到该值};});
}