promisequeue.js

var request = require('request');

var promiseFunction = function(){
  return new Promise(function(resolve, reject){
    request.get('http://google.com', function(e, r, b){
      console.log('got');
      resolve();
    });
  });
}

var promises = [];

for(var i = 0; i < 20; i++){
  promises.push(promiseFunction);
}

function queuePromises(in_promises, rate){
  return new Promise(function(resolve, reject){
    var promises = in_promises;
    var activePromises = 0;
    var cur = 0;
    next();
    function next(){
      while(activePromises < rate){
        if(cur < promises.length){
          activePromises++;
          promises[cur]().then(function(result){
            activePromises--;
            if(cur < promises.length){
              next();
            }
          })
          cur++;
        } else {
          return resolve(result);
          break;
        }
      }
    }
  })
}

queuePromises(promises, 1)
.then(function(result){
  console.log('done');
})