files.js

const files = [/* file names here */];
const limit = 100;

async function main() {
  const workers = [];
  while(workers.length <= limit) {
    const w = worker(files);
    workers.push(w);
  }

  await Promise.all(workers);
}

async function worker(files) {
  while(files.length) {
    const file = files.shift();
    await processFile(file);
  }
}

async function processFile(file) {
  return new Promise(done => {
    // process file and call done at the end
    // alternatively use async/await file functions
  });
}