One way would be to convert the arrays to JSON strings, then use a Set to get unique values, and convert back again
var arr = [
[1, 1, 2],
[1, 2, 1],
[1, 1, 2],
[1, 2, 1],
[2, 1, 1],
[2, 1, 1]
];
let set = new Set(arr.map(JSON.stringify));
let arr2 = Array.from(set).map(JSON.parse);
console.log(arr2)