数组去重的六种方法

 1、创建一个空数组，判断旧数组元素是否在新数组中，不存在则将旧数组的元素放入新数组中，直至遍历完旧数组。

  var arr1 = [1,5,5,8,8,9,2,3,3];
  var arr2 = [];
  for(var i = 0; i < arr1.length; i++) {
    if (arr2.indexOf(arr1[i]) == -1) {
      arr2.push(arr1[i]);
    }
  }
  console.log(arr2);

2、冒泡比较 ，即比较相邻的元素，不一样则将后一个元素放入空数组

  var arr = [1,5,5,8,8,9,2,3,3];
  function fn1(arr) {
    var newArr=[arr[0]];
    for (let i = 1; i < arr.length; i++) {
      if (arr[i]!==arr[i-1]) {
        newArr.push(arr[i]);
      }
    }
    return newArr;
  }
  console.log(fn1(arr));

3、利用对象属性不重复的性质

var arr = [1,5,5,8,8,9,2,3,3];
  function fn2(arr) {
    var obj = {};
    var newArr = [];
    for (let i = 0; i < arr.length; i++) {
      if (!obj[arr[i]]) {
         obj[arr[i]] = 1;
         newArr.push(arr[i]);
      }   
    }
    return newArr;
  }
  console.log(fn2(arr));

4、利用includes方法 

var arr = [1,5,5,8,8,9,2,3,3];
  function fn3(arr) {
    var newArr = [];
    for (var i = 0; i < arr.length; i++) {
      if (!newArr.includes(arr[i])) {
         newArr.push(arr[i]);
      }
    }
    return newArr;
  }
  console.log(fn3(arr));

5、利用for循环配合splice方法 

var arr = [1,5,5,8,8,9,2,3,3] 
  function fn4(arr) {
    for (let i = 0; i < arr.length; i++) {
      for (let j = i + 1; j < arr.length; j++) {
        if (arr[i] === arr[j]) {
          arr.splice(j,1)
          j--
        }
      }
    }
    return arr
  }
  console.log(fn4(arr))

 6、 利用set对象的特性

var arr = [1,5,5,8,8,9,2,3,3]
function fn5(arr) {
  return Array.from(new Set(arr));
}
console.log(fn5(arr))