前端压缩base64格式图片

封装成js文件，随时都可以调用

var dealImage = (base64, w, callback) => {
        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100kb以下，请加以下语句，quality初始值根据情况自定
            while (base64.length / 1024 > 100) {
                quality -= 0.01;
                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
        }
    }

export default dealImage        

在页面中调用

import dealImage from ''

let printing = (base64) => {    
    console.log(base64.length)
    //获取压缩后的base64大小
}

dealImage('你的图片地址', 800, printing);