node imagemagick batch resizing multithread

batch-resizer.js

// Batch image resizing with Node Imagemagick
// author: Rungsikorn Rungsikavanich
// contact: rungsikorn@me.com

// Dependencies ( Need native imagemagick )
// $ brew install imagemagick 
// $ npm i imagemagick lodash
// example: `$  DIR=../static/images/stock/herbarium-original node ./lib/batch-resizer.js`
// result image will be locate in ./resize folder
const im = require('imagemagick');
const fs = require('fs');
const path = require('path');
const _ = require('lodash');

// DIR is Relative from script location
const images = fs.readdirSync(path.join(__dirname, process.env.DIR || '.'));
// P is number of parallel threads
const threads = parseInt(process.env.P, 10) || 20;

const imagesList = images;

(async function () {
  for (let index = 0; index < imagesList.length - 1; index += threads) {
    console.log(`parallel resizing started at index: ${index}`);
    const q = _.range(index, index + threads, 1)
      .map(async (i) => {
        const imageName = imagesList[i];
        try {
          if (imageName) {
            const imagePath = path.join(__dirname, process.env.DIR || '.', imageName);
            const dstPath = path.join(__dirname, process.env.DIR || '.', 'resize', `${path.basename(imageName)}`);
            const ext = path.extname(imageName);
            if (ext.toLowerCase() === '.jpg') {
              const resizePromise = new Promise((rs) => {
                im.resize({
                  srcPath: imagePath,
                  dstPath,
                  width: 1024,
                }, () => {
                  console.log(`${i}/${images.length} (${imageName})`);
                  rs();
                });
              });
              await resizePromise;
            }
          }
        } catch (e) {
          console.log(`error${imageName}`);
          console.log(e);
        }
      });
    await Promise.all(q);
  }
}());