这些功能代码，让你成为前端专家

1. 数组去重

const numbers =[1, 1, 1, 2, 3, 2, 4]

let array = Array.from(new Set(numbers)); 
console.log(array); // Result: [1, 2, 3, 4]

或

let array = [...new Set(numbers)]; 
console.log(array); // Result: [1, 2, 3, 4]

2. 数组求和

const arr = [1,2,3,4,5,6,7]
const sum = arr.reduce((pre,cur)=>{
return pre +cur
})
console.log(sum)
//Result:28

3. 获取一个随机布尔值 (true/false)

const randomBoolean = () => Math.random() >= 0.5;
console.log(randomBoolean());
// Result: a 50/50 change on returning true of false

4. 检查日期是否为工作日

const isWeekday = (date) => date.getDay() % 6 !== 0;
console.log(isWeekday(new Date(2021, 0, 11)));
// Result: true (Monday)
console.log(isWeekday(new Date(2021, 0, 10)));
// Result: false (Sunday)

5. 反转字符串

const reverse = str => str.split('').reverse().join('');
reverse('hello world');     
// Result: 'dlrow olleh'

6. 检查当前 Tab 页是否在前台

const isBrowserTabInView = () => document.hidden;
isBrowserTabInView();
// Result: returns true or false depending on if tab is in view / focus

7. 检查数字是否为奇数

const isEven = num => num % 2 === 0;
console.log(isEven(2));
// Result: true
console.log(isEven(3));
// Result: false

8. 从日期中获取时间

const timeFromDate = date => date.toTimeString().slice(0, 8);
console.log(timeFromDate(new Date(2021, 0, 10, 17, 30, 0))); 
// Result: "17:30:00"
console.log(timeFromDate(new Date()));
// Result: will log the current time

9. 保留小数点（非四舍五入）

const toFixed = (n, fixed) => ~~(Math.pow(10, fixed) * n) / Math.pow(10, fixed);
// Examples
toFixed(25.198726354, 1);       // 25.1
toFixed(25.198726354, 2);       // 25.19
toFixed(25.198726354, 3);       // 25.198
toFixed(25.198726354, 4);       // 25.1987
toFixed(25.198726354, 5);       // 25.19872
toFixed(25.198726354, 6);       // 25.198726

10. 检查元素当前是否为聚焦状态

const elementIsInFocus = (el) => (el === document.activeElement);
elementIsInFocus(anyElement)
// Result: will return true if in focus, false if not in focus

11. 检查浏览器是否支持触摸事件

const touchSupported = () => {
  ('ontouchstart' in window || window.DocumentTouch && document instanceof window.DocumentTouch);
}
console.log(touchSupported());
// Result: will return true if touch events are supported, false if not

12. 检查当前用户是否为苹果设备

const isAppleDevice = /Mac|iPod|iPhone|iPad/.test(navigator.platform);
console.log(isAppleDevice);
// Result: will return true if user is on an Apple device

13. 滚动到页面顶部

const goToTop = () => window.scrollTo(0, 0);
goToTop();
// Result: will scroll the browser to the top of the page

14. 获取所有参数平均值

const average = (...args) => args.reduce((a, b) => a + b) / args.length;
average(1, 2, 3, 4);
// Result: 2.5

15. 转换华氏度/摄氏度

const celsiusToFahrenheit = (celsius) => celsius * 9/5 + 32;
const fahrenheitToCelsius = (fahrenheit) => (fahrenheit - 32) * 5/9;
// Examples
celsiusToFahrenheit(15);    // 59
celsiusToFahrenheit(0);     // 32
celsiusToFahrenheit(-20);   // -4
fahrenheitToCelsius(59);    // 15
fahrenheitToCelsius(32);    // 0

16. 将任何值转换成布尔值

使用双感叹号(!!)能将任何内容转换成布尔值

!!true    // true
!!2       // true
!![]      // true

!!false   // false
!!0       // false
!!" "     // false

17. 扩展运算符

连接两个数组数组

const nums1 = [1,2,3]
const nums2 = [4,5,6]

newArray = [...nums1 ,...nums2 ]   //[1,2,3,4,5,6]

也可以将值推送到数组

let  numbers =  [1,2,3]

numbers = [...numbers , 4, 5] //[1,2,3,4,5]

18. 检查一个项目是否存在于数组中

let arrs = [1,2,3];

const hasNumber = arrs.indexOf(1) > -1   //true

或

const hasNumbers = arrs.includes(1)   //true

19. 避免使用长||检查多个条件链

const nums = 1

if(num == 1 || num == 2 || num == 3){
   console.log('true')
}

更简便方法

if([1,2,3].includes(num)){   
   console.log('true')
}

20. 数组扁平化

多维数组=>一维数组 
let arr = [1, [2, [3, [4, 5]]], 6];
let str = jsON.stringify(ary);

1.arr.flat(Infinity);//注意：flat和flatMap方法为ES2019(ES10)方法，目前还未在所有浏览器完全兼容。

2.str.replace(/([]))/g, '').split(',');

3.str = str.replace(/([]))/g, '');
str = '[' + str + ']';
var ary = jsON.parse(str);

21. 数字化整数

const DigitizeInt = n => [...`${n}`].map(i => parseInt(i));
DigitizeInt(4560) // [4, 5, 6, 0]
DigitizeInt(131) // [1,3,1]

22. 修剪空格

let string = " a b    cd   e   ";
let Trim = string.replace(/s+/g, '');
console.log(Trim)

24. 筛选出有相同key的对象

let namelist = [{
  name: 'mark',
  age: 15,
  hair: 'long'
}, {
  name: 'tuwen',
  age: 16,
  hair: 'short'
}, {
  name: 'xiaoming',
  age: 16,
  hair: 'short'
}, {
  name: 'lilei',
  age: 15,
  hair: 'short'
}, {
  name: 'hanmei',
  age: 17,
  hair: 'long'
}]

ES6

let map = new Map()

namelist.forEach(item => {
    if (map.has(item.age)) {
        map.set(item.age, map.get(item.age).concat(item))
    } else {
        map.set(item.age, [item]) 
    }
})

console.log(map)

const [arr1, arr2, arr3] = [...map]

结果

arr_1 = [{
  name: 'mark',
  age: 15,
  hair: 'long'
}, {
  name: 'lilei',
  age: 15,
  hair: 'short'
}]

arr_2 = [{
  name: 'tuwen',
  age: 16,
  hair: 'short'
}, {
  name: 'xiaoming',
  age: 16,
  hair: 'short'
}]

arr_3 = [{
  name: 'hanmei',
  age: 17,
  hair: 'long'
}]