Explaining sync code and slow io operation

1-sync-js-starving-example.js

var alert = console.info;
console.time('APP_CALL');
function firstAPI() { 
  alert('first api call'); 
  var i =0;
  var looptillIndex_sm =1000000;
  var looptillIndex_lg =1000000000;
  console.time('API_CALL')
  //SyncIo
  while(i <  looptillIndex_lg-1){
  //while(i <  looptillIndex_sm-1){
      
      //one of the worst thing that you can do...Log...
      if(i%1000000 ==0) console.log("i m here..", i);
      i++;
  }
  console.timeEnd('API_CALL')
}
function secAPI() { 
  alert('sec api call...');
  console.timeEnd('APP_CALL');
}
setTimeout(firstAPI, 1000);
setTimeout(secAPI, 1002);