1 function unique(arr) {
2     return Array.from(new Set(arr));
3 }

 1 function unique(arr) {
 2     for (let i = 0; i < arr.length; i++) {
 3         for (let j = i + 1; j < arr.length; j++) {
 4             if (arr[i] === arr[j]) {
 5                 arr.splice(j, 1);
 6                 j--;
 7             }
 8         }
 9     }
10 
11     return arr;
12 }

1 function unique(arr) {
2     return arr.reduce((accumulator, currentValue) => accumulator.includes(currentValue) ? accumulator : [...accumulator, currentValue], []);
3 }

 1 function unique(arr) {
 2     let res = [];
 3     for (let i = 0; i < arr.length; i++) {
 4         if (res.indexOf(arr[i]) === -1) {
 5             res.push(arr[i]);
 6         }
 7     }
 8 
 9     return res;
10 }

 1 function unique(arr) {
 2     let res = [];
 3     if (arr.length < 1) {
 4         return res;
 5     }
 6 
 7     arr.sort(); res.push(arr[0]);
 8     for (let i = 1; i < arr.length; i++) {
 9         if (arr[i] !== arr[i-1]) {
10             res.push(arr[i]);
11         }
12     }
13 
14     return res;
15 }

 1 function unique(arr) {
 2     let res = [], map = new Map();
 3     for (let i = 0; i < arr.length; i++) {
 4         if (!map.has(arr[i])) {
 5             res.push(arr[i]);
 6             map.set(arr[i], 1);
 7         } else {
 8             map.set(arr[i], map.get(arr[i]) + 1);
 9         }
10     }
11     
12     return res;
13 }

1 function unique(arr) {
2     return arr.filter((currentValue, currentIndex) => {
3         return arr.indexOf(currentValue) === currentIndex;
4     })
5 }