Best way to write loops with promises (ctx.sync) in JavaScript API for Office

There are many threads that discuss about guaranteeing execution order of promises in loops. I would like to know what is the best practice in JavaScript API for Office Add-ins. Most of the time, the promise in question is ctx.sync().

Here is a snippet to print the address of a list of Excel ranges one by one. The test shows that it respects well the order of Excel ranges. But the question is whether and how to guarantee the execution order?

function loadAll () {
   var ranges = ["A:A", "B:B", "C:C", "D:D", "E:E"];
   var sheet = "Sheet1";
   for (var i = 0; i < ranges.length; i++) {
       loadRange(ranges[i], sheet);        
   }
}

function loadRange (range, sheet) {
   Excel.run(function (ctx) { 
       var r = ctx.workbook.worksheets.getItem(sheet).getRange(range);
       r.load('address');
       return ctx.sync().then(function() {
          console.log(r.address);
       });
   });
}

Could anyone help?