javascript中的数组去重

1. 双层循环

const unique = array => {
  const res = [];
  for (let i = 0; i < array.length; i++) {
    const arrValue = array[i];
    for (var j = 0; j < res.length; j++) {
      const resValue = res[j];
      if (arrValue === resValue) {
        break;
      }
    }
    if (j === res.length) {
      res.push(arrValue)
    }
  }
  return res;
}

2.indexOf

const unique = array => {
    const res = [];
    for (let i = 0, len = array.length; i < len; i++) {
        const current = array[i];
        if (res.indexOf(current) === -1) {
            res.push(current)
        }
    }
    return res;
}

3.filter

const unique = array => array.filter((item, index, array) => array.indexOf(item) === index)

4.Object健值对

const unique = array => {
  const obj = {};
  return array.filter(function(item, index, array){
      return obj.hasOwnProperty(typeof item + JSON.stringify(item)) 
        ? false
        : (obj[typeof item + JSON.stringify(item)] = true)
  })
}
const array = [{value: 1}, {value: 1}, {value: 2}, 2, 1, "1", "2", null, null, undefined, undefined, NaN, NaN];
// [ { value: 1 }, { value: 2 }, 2, 1, '1', '2', null, undefined, NaN ]
console.log(unique(array));

5.Set

const unique = array => [...new Set(array)];

6.Map

const unique = array => {
  const map = new Map();
  return array.filter(a => !map.has(a) && map.set(a, 1));
};