Wrapper to ensure an async function runs in series when called multiple times

gatedAsync.js

function gatedAsync(fn) {
  var running = false, queue = [];
  return function(...args) {
    if(running) {
      queue.push([run, args]);
    } else {
      run(...args);
    }

    function run(...args) {
      running = true;
      fn(...args, function() {
        var next = queue.shift();
        if(next) {
          process.nextTick(() => {
            var [f, args] = next;
            f(...args);
          });
        }
        running = false;
      });
    }
  }
}