JS去重总结

最近面试几次问到去重,回答的不是很好,总结下

双重循环

实现比较容易,代码略微繁琐

Array.prototype.unique = function () {
  const newArray = [];
  let isRepeat;
  for (let i = 0; i < this.length; i++) {
    isRepeat = false;
    for (let j = 0; j < newArray.length; j++) {
      if (this[i] === newArray[j]) {
        isRepeat = true;
        break;
      }
    }
    if (!isRepeat) {
      newArray.push(this[i]);
    }
  }
  return newArray;
}

indexOf

1. 利用filter()

Array.prototype.unique = function () {
  return this.filter((item, index) => {
    return this.indexOf(item) === index;
  })
}

2. forEach

Array.prototype.unique = function () {
  const newArray = [];
  this.forEach(item => {
    if (newArray.indexOf(item) === -1) {
      newArray.push(item);
    }
  });
  return newArray;
}

sort()

先排序,再比较

Array.prototype.unique = function () {
  const newArray = [];
  this.sort();
  for (let i = 0; i < this.length; i++) {
    if (this[i] !== this[i + 1]) {
      newArray.push(this[i]);
    }
  }
  return newArray;
}

reduce()

Array.prototype.unique = function () {
  return this.sort().reduce((init, current) => {
    if(init.length === 0 || init[init.length - 1] !== current){
      init.push(current);
    }
    return init;
  }, []);
}

键值对

利用对象key 不同

Array.prototype.unique = function () {
  const newArray = [];
  const tmp = {};
  for (let i = 0; i < this.length; i++) {
    if (!tmp[typeof this[i] + this[i]]) {
      tmp[typeof this[i] + this[i]] = 1;
      newArray.push(this[i]);
    }
  }
  return newArray;
}

includes()

Array.prototype.unique = function () {
  const newArray = [];
  this.forEach(item => {
    if (!newArray.includes(item)) {
      newArray.push(item);
    }
  });
  return newArray;
}

map()

Array.prototype.unique = function () {
  const tmp = new Map();
  return this.filter(item => {
    return !tmp.has(item) && tmp.set(item, 1);
  })
}

set()

Array.prototype.unique = function () {
  return [...new Set(this)];
}

总结

map和set去重速度快于其他方法,es5的方法兼容好一些