JavaScript中的数组去重

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

function unique(arr) {
  let res = arr.filter(function (item, index, array) {
    return arr.indexOf(item) === index;
  });
  return res;
}

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

function unique(arr) {
  const last = new Map();
  return arr.filter((item) => !last.has(item) && last.set(item, 1));
}