How to separate each sub group in main group Array using javascript

Question

I have an Array. It contains several subgroups. Example:

let mainArray=[50,51,52,53,54,511,512,513,514,521,522,523,524,525,526,527]

I want

Answer 1

var arr = [50,51,52,53,54,511,512,513,514,521,522,523,524,525,526,527];
var result = [],
    lastVal = -1;
while(arr.length) {
  var currentIndex = arr.length - 1;
  var currentValue = arr[currentIndex];
  var c = Math.floor(currentValue/10);
  if (c !== lastVal) {
    lastVal = c;
    result.push([currentValue]);
  }else{
    result[result.length-1].push(currentValue);
  }
  arr.splice(currentIndex, 1);
}
result.forEach(function(arr){ arr.reverse(); });
console.log(result);