function doSomething(id) {
  return new Promise(function(resolve,reject){
                setTimeout(() => {
                              console.log(id+') Stage 1')
                              resolve(id)
                            }, Math.random()*100)

              }).then(function(data){
                  setTimeout(() => console.log(data+') Stage 2'),Math.random()*100)
            })
}

for(var i=0;i<100;i++){
  doSomething('op'+i)
}