// 演示代码
function unique(arr) {
  /* your code */
}

let strings = ["Hare", "Krishna", "Hare", "Krishna",
  "Krishna", "Krishna", "Hare", "Hare", ":-O"
];

alert( unique(strings) ); // Hare, Krishna, :-O

1.通过ES6用Set去重

function unique(arr) {
  return [...new Set(arr)];
}

2.使用数组的方法indexOf

function unique(arr) {
  let hash = [];
  for (let i = 0; i < arr.length; i++) {
    if (hash.indexOf(arr[i]) === -1) {
      hash.push(arr[i]);
    }
  }
  return hash;
}

3.排序后比较相邻元素

function unique(arr) {
	arr.sort();
  let hash = [];
  for (let i = 0; i < arr.length; i++) {
    if (arr[i] !== arr[i + 1]) {
      hash.push(arr[i]);
    }
  }
  return hash;
}