Array.prototype.sort() 적용

var items = [
  { name: 'Edward', value: 21 },
  { name: 'Sharpe', value: 37 },
  { name: 'And', value: 45 },
  { name: 'The', value: -12 },
  { name: 'Magnetic' },
  { name: 'Zeros', value: 37 }
];

// sort by value
items.sort(function (a, b) {
  return (a.value - b.value)
});

// sort by name
items.sort(function(a, b) {
  var nameA = a.name.toUpperCase(); // ignore upper and lowercase
  var nameB = b.name.toUpperCase(); // ignore upper and lowercase
  if (nameA < nameB) {
    return -1;
  }
  if (nameA > nameB) {
    return 1;
  }

  
// names must be equal

  return 0;
});

//        2, 2, 2  1, 1, 1    [1, 1, 1, 2, 2, 2]
//   [1,2,1,2,1,3,4,5,4,5,5,2,2] => [3, 4, 4, 1, 1, 1, 5, 5, 5, 2, 2, 2, 2]

let arr = [9, 7, 7, 1, 2, 1, 2, 1, 3, 4, 5, 4, 5, 5, 2, 2];
function sortArray(arr) {
    let obj = {};
    let newArr = [];
    for(let i = 0; i < arr.length; i++) {
      let cur = arr[i];
      if(obj[cur]){
        obj[cur].push(cur);
        continue;
      }
      obj[cur] = [cur];
    }
    for(let k in obj) {
      if(obj.hasOwnProperty(k)) {
        newArr.push(obj[k])
      }
    }
    newArr.sort((a, b) => {
      if(a.length === b.length){
        return a[0] - b[0];
      }
        return a.length - b.length;
    });
    newArr = newArr.reduce((prev, cur) => prev.concat(cur));
    return newArr;
  }
  console.log(sortArray(arr)); // [ 3, 9, 4, 4, 7, 7, 1, 1, 1, 5, 5, 5, 2, 2, 2, 2 ]

 ： 
 ：https://juejin.im/post/5aa7d82c6fb9a028c522de43
 ： 
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