js 数组笔记

浅复制

const arr = [1, 3, 4, 5, 6, 7, 8];
const newArr = arr;

console.log(`arr: ${arr}`);                   // arr: 1,3,4,5,6,7,8
console.log(`newArr: ${newArr}`);             // arr: 1,3,4,5,6,7,8

// 原数组改变，新数组也会跟着改变，因为这里的是浅复制，仅仅是point指向arr
arr.length = 4;

console.log(`arr: ${arr}`);                   // arr: 1,3,4,5
console.log(`newArr: ${newArr}`);             // newArr: 1,3,4,5

深复制

const arr = [1, 3, 4, 5, 6, 7, 8];
const newArr = arr.map(arr=>arr);             // map 会输出一个新的数组
// const newArr = [...arr];                   // 用es6的spread  传播的扩展数组方式形成一个新数组也是一样的
console.log(`arr: ${arr}`);                   // arr: 1,3,4,5,6,7,8
console.log(`newArr: ${newArr}`);             // newArr: 1,3,4,5,6,7,8

// 原数组改变，新数组不变
arr.length = 4;

console.log(`arr: ${arr}`);                   // arr: 1,3,4,5
console.log(`newArr: ${newArr}`);             // newArr: 1,3,4,5,6,7,8

数组shift()方法的实用性

假如数组没有 Array.prototype.shift()这种方法，我们如何[1,2,3,4,5,6] => [2,3,4,5,6]?那就会变得非常麻烦.

var arr  =[1,2,3,4,5,6];
var newArr = [];
for(var i=0;i<arr.length;i++){
    newArr[i]=arr[i+1]
}
newArr=[2,3,4,5,6,]     // arr 最后一个数组为null

数组排序, 根据id排序

const Arr = [
  { id: 1, name: 'peng' },
  { id: 0, name: 'zhou' },
  { id: 2, name: 'huang' },
];
// 运用es6的方法轻易做到
const newArr = Arr
  .map(e => e.id)
  .sort()
  .map(id => Arr.find(arr => arr.id === id));
console.log(newArr);

第二种方法

const by = (name, minor) => (o, p) => {
  const a = o[name];
  const b = p[name];

  if (a === b) {
    minor(o, p);
  }
  return a < b ? -1 : 1;
};
// 测试数据
$.ajax({
  url: 'https://chat.pipk.top/graphql',
  type: 'POST',
  dataType: 'json',
  data: {
    query: `{
      search(query:"yinxin630" , type:USER,first:1){
        edges{
          node{
            ... on User{
              repositories(first:100){
                nodes {
                  forkCount
                  createdAt
                  updatedAt
                  name
                }
              }
            }
          }
        }
      }
    }`,
  },
  success(json) {
    const Arr = json.data.search.edges[0].node.repositories.nodes;
    // 根据createAt排序，如果createAt相同，则根据forkCount排序
    const newArr = Arr.sort(by('createdAt', by('forkCount')));
    console.log(newArr);
  },
});

数组去重

const Arr = [1, 2, 3, 4, 23, 5, 5, 5, 6, 6, 4];
const newArr = new Set();
Arr.forEach(arr => newArr.add(arr));
console.log(newArr);