数组去重

一、forEach、some

---

function is(x, y) {
  if (x === y) {
    return x !== 0 || y !== 0 || 1 / x === 1 / y;
  } else {
    return x !== x && y !== y;
  }
}

function unique(array) {
  const result = [];

  array.forEach((value) => {
    if (!result.some((v) => is(v, value))) {
      result.push(value);
    }
  });

  return result;
}

二、reduce、some

---

function is(x, y) {
  if (x === y) {
    return x !== 0 || y !== 0 || 1 / x === 1 / y;
  } else {
    return x !== x && y !== y;
  }
}

function unique(array) {
  return array.reduce((prev, curr) => {
    return prev.concat(prev.some((v) => is(v, curr)) ? [] : [curr]);
  }, []);
}

三、filter、findIndex

---

function is(x, y) {
  if (x === y) {
    return x !== 0 || y !== 0 || 1 / x === 1 / y;
  } else {
    return x !== x && y !== y;
  }
}

function unique(array) {
  return array.filter((value, index) => {
    return array.findIndex((_value) => is(_value, value)) === index;
  });
}

四、Set

---

function unique(array) {
  return Array.from([...new Set(array)]);
}

五、对象属性

---

function unique(array) {
  const result = [];
  const resultMap = {};
  const length = array.length;
  for (let i = 0; i < length; i++) {
    if (!Object.prototype.hasOwnProperty.call(resultMap, array[i])) {
      resultMap[array[i]] = true;
      result.push(array[i]);
    }
  }
  return result;
}

六、Map 键值

---

function unique(array) {
  const result = [];
  const map = new Map();
  const length = array.length;
  for (let i = 0; i < length; i++) {
    if (!map.has(array[i])) {
      map.set(array[i], true);
      result.push(array[i]);
    }
  }
  return result;
}

七、测试数据

---

const array = [
  34,
  23,
  53,
  23,
  53,
  "张文强",
  "张文强",
  null,
  null,
  undefined,
  undefined,
  {},
  {},
  23,
  "张文强",
  34,
  NaN,
  NaN,
];

const result = unique(array);
console.log(result);