fatArrow.js

//Simple Class function
function API() {
  this.name = 'This is API name';
}

//prototype function for share between the object
API.prototype.getName = function() {
  
  //Take copy of this keyword
  var self = this; 
  return new Promise( function(resolve, reject){
    
    resolve(self.name); 
    //resolve(this);  // [Object window]
    
  });
}

//for Fat-Arrow function with this keyword
API.prototype.getNamewithArrowFun = function() {
  
  return new Promise( (resolve, reject) => {
    
    resolve(this.name); 
    //resolve(this);  // [Object window]
    
  });
}


//create object using new keyword. It is a constructor function.
var api = new API();

api.getName().then( data =>  console.log(data)); //"This is API name"
 
api.getNamewithArrowFun().then( data =>  console.log(data)); //"This is API name"