js base64图片压缩

js 图片 压缩 图片 js

function 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);
        // }
        callback(base64);//必须通过回调函数返回，否则无法及时拿到该值
    }
}



//这是原来的base64格式字符串
var base64= path;
//这就是你压缩之后的字符串
var str;
//你可以打桩看一下有多长
console.log(base64.length);
//然后调用压缩方法 第一个参数就是原来的字符串，第二个是宽度，第三个就是回调方法，也就是压缩函数最后面那个callback（base64）
dealImage(base64, 500, useImg);
//然后一压 再打个桩看下长度 方法名随便起怎么舒服怎么来
function useImg(base64) {
    str= base64;
    console.log(str.length);
}

https://blog.csdn.net/zx19930309/article/details/90375907