nodejs 压缩本地图片，转换为 base64。

img-compress.js

const fs = require('fs');
const Canvas = require('canvas');

function compress(buff) {
     // 将文件绘制成图片对象
     let image = new Canvas.Image;
     image.src = buff;

     // 获取原始图片宽高
     let drawWidth=image.width;
     let drawHeight=image.height;

     // 以下改变一下图片大小
     var maxSide = Math.max(drawWidth, drawHeight);
     if (maxSide > 600) {
           var minSide = Math.min(drawWidth, drawHeight);
            minSide = minSide / maxSide * 1024;
            maxSide = 600;
           if (drawWidth > drawHeight) {
                drawWidth = maxSide;
                drawHeight = minSide;
            } else {
                drawWidth = minSide;
                drawHeight = maxSide;
            }
    }

    // 用 canvas 重绘
    let canvas = new Canvas(drawWidth, drawHeight);
    let context=canvas.getContext('2d');
    context.drawImage(image, 0, 0, drawWidth,drawHeight);

    // 压缩0.5就是压缩百分之50
    canvas.toDataURL('image/jpeg', 0.7, (err, jpeg) => {
        // 压缩后的数据写入文件
        fs.writeFile('result.txt', jpeg, (err) => {
            if (err) throw err;
            console.log('It\'s saved!');
        });
    });
}

fs.readFile('WechatIMG3836.png', (err, sq) => {compress(sq)})

perfect！