今天，学会这10个JS代码段就够了！

用 apply 将数组各项添加到另一个数组

const array = ['a', 'b'];
const elements = [0, 1, 2];
array.push.apply(array, elements);
console.info(array); // ["a", "b", 0, 1, 2]

函数只执行一次

function once (fn){
  let called = false
  return function () {
    if (!called) {
      called = true
      fn.apply(this, arguments)
    }
  }
}

function func (){
    console.log(1);
}

//调用
let onlyOnce = once(func);

// 测试
onlyOnce(); // 1
onlyOnce(); // 不执行

防抖

/**
 * 防抖
 * @param {Function} func 要执行的回调函数
 * @param {Number} wait 延时的时间
 * @param {Boolean} immediate 是否立即执行
 * @return null
 */
let timeout;
function Debounce(func, wait = 3000, immediate = true) {
  // 清除定时器
  if (timeout !== null) clearTimeout(timeout);
  // 立即执行，此类情况一般用不到
  if (immediate) {
    var callNow = !timeout;
    timeout = setTimeout(function() {
      timeout = null;
    }, wait);
    if (callNow) typeof func === 'function' && func();
  } else {
    // 设置定时器，当最后一次操作后，timeout不会再被清除，所以在延时wait毫秒后执行func回调方法
    timeout = setTimeout(function() {
      typeof func === 'function' && func();
    }, wait);
  }
}

Debounce(()=>console.log(1));

递归数组降为一维

let children = [1, [2, 3], [4, [5, 6, [7, 8]]], [9, 10]];
function simpleNormalizeChildren(children) {
            for (let i = 0; i < children.length; i++) {
                if (Array.isArray(children[i])) {
                    children = Array.prototype.concat.apply([], children);
                    simpleNormalizeChildren(children)
                }
            }
            return children;
        }

console.log(simpleNormalizeChildren(children)); // [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

数组降维(二维降一维)

function simpleNormalizeChildren(children) {
            for (let i = 0; i < children.length; i++) {
                if (Array.isArray(children[i])) {
                    return Array.prototype.concat.apply([], children)
                }
            }
            return children
}
let arrs = [['1'],['3']];
const arr = simpleNormalizeChildren(arrs);
console.log(arr); // ['1','3']

使用可选链进行函数调用

function doSomething(onContent, onError) {
  try {
   // ... do something with the data
  }
  catch (err) {
    onError?.(err.message); // 如果onError是undefined也不会有异常
  }
}

检测数组对象中是否有空值

const data = [
  {
  	name:"maomin"
  },
  {
    name:""
  }
]
const arr = data.filter(item =>
    Object.values(item).includes('')
);

console.log(arr.length>0?"有空值":"无空值"); // 有空值

计算数组中每个元素出现的次数

let names = ['Alice', 'Bob', 'Tiff', 'Bruce', 'Alice'];

let countedNames = names.reduce(function (allNames, name) {
  if (name in allNames) {
    allNames[name]++;
  }
  else {
    allNames[name] = 1;
  }
  return allNames;
}, {});

console.log(countedNames); //  { Alice: 2, Bob: 1, Tiff: 1, Bruce: 1 }

按属性对object分类

let people = [
  { name: 'Alice', age: 21 },
  { name: 'Max', age: 20 },
  { name: 'Jane', age: 20 }
];

function groupBy(objectArray, property) {
  return objectArray.reduce(function (acc, obj) {
    let key = obj[property];
    if (!acc[key]) {
      acc[key] = [];
    }
    acc[key].push(obj);
    return acc;
  }, {});
}

const groupedPeople = groupBy(people, 'age');
console.log(groupedPeople);
// {
//   20: [
//     { name: 'Max', age: 20 },
//     { name: 'Jane', age: 20 }
//   ],
//   21: [{ name: 'Alice', age: 21 }]
// }

将带有分割符的字符串转化成一个n维数组

 const str = "A-2-12";
 const str1 = str.split('-');
 console.log(str1);
 const arr = str1.reverse().reduce((pre,cur,i) => {
 if(i==0)
  { pre.push(cur)
   return pre
 }
  return [cur,pre]
},[])
 
console.log(arr) // ["A"["B",["C"]]]