files.js

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

async function main() {
  var runningWorkers = 0;

  function continuationHandler() {
    runningWorkers--;
    loadWorkers();    
  }
  
  function pickItem() {
    const file = files.shift();
    if (file) {
      runningWorkers++;
      // continue in any case      
      worker(file).then(continuationHandler, continuationHandler);
    }
  }
  
  function loadWorkers() {
    do {
      pickItem();
    } while(runningWorkers < limit)
  }
  
  loadWorkers();
}

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