How deferred chaining works ?

deferred_chain.js

var performParent = function(){
    //perform 1st async
    var promise1 = performAsync('func1',5);
  
    // We want to chain two async operations
    promise1.then(function(data){ 
      
        console.log('data from 1st async operation',data);
        //perform second async operation

        //this return links second aync deferred to first one
        return performAsync('func2',10); 
      
    }).then(function(data){
          console.log('finalData',data); 
          console.log('both done');
    });
};

var performAsync = function(nameStr,count){
   
    var deferred = $.Deferred();
  
    var intervalId = window.setInterval(function(){
      --count;
      if(count==0){
          clearInterval(intervalId);
          deferred.resolve({idea:nameStr});
          return;
      }
      console.log(nameStr+':'+count);
      
    }, count*100);
  
    return deferred.promise();
};