前端开发技巧

字符串技巧

1、比较时间

const time1 = "2022-03-02 09:00:00";
const time2 = "2022-03-02 09:00:01";
const overtime = time1 < time2;
// overtime => true

2、格式化money

const ThousandNum = num => num.toString().replace(/\B(?=(\d{3})+(?!\d))/g, ",");
const money = ThousandNum(1000000);
// money => '1,000,000'

3、生成随机ID

const RandomId = len => Math.random().toString(36).substr(3, len);
const id = RandomId(10);
// id => "xdeguewg1f"

4、生成随机 HEX 颜色值

const RandomColor = () => "#" + Math.floor(Math.random() * 0xffffff).toString(16).padEnd(6, "0");
const color = RandomColor();
// color => "#2cbf89"

5、Generate star ratings

const StartScore = rate => "★★★★★☆☆☆☆☆".slice(5 - rate, 10 - rate);
const start = StartScore(3);
// start => '★★★☆☆'

6、网址查询参数

const params = new URLSearchParams(location.search.replace(/\?/ig, "")); // location.search = "?name=test&sex=man"
params.has("test"); // true
params.get("sex"); // "man"

数字技能

7、Arrangement

用 Math.floor() 代替正数，用 Math.ceil() 代替负数

const num1 = ~~ 1.19;
const num2 = 2.29 | 0;
const num3 = 3.09 >> 0;
// num1 num2 num3 => 1 2 3

8、零填充

const FillZero = (num, len) => num.toString().padStart(len, "0");
const num = FillZero(1234, 5);
// num => "01234"

9、转数

仅对 null、“”、false、数字字符串有效

const num1 = +null;
const num2 = +"";
const num3 = +false;
const num4 = +"169";
// num1 num2 num3 num4 => 0 0 0 169

10、时间戳

const timestamp = +new Date("2022-03-22");
// timestamp => 1647907200000

11、精确小数

const RoundNum = (num, decimal) => Math.round(num * 10 ** decimal) / 10 ** decimal;
const num = RoundNum(1.2345, 2);
// num => 1.23

12、平价

const OddEven = num => !!(num & 1) ? "odd" : "even";
const num = OddEven(2);
// num => "even"

13、取最小值最大值

const arr = [0, 1, 2, 3];
const min = Math.min(...arr);
const max = Math.max(...arr);
// min max => 0 3

14、生成范围随机数

const RandomNum = (min, max) => Math.floor(Math.random() * (max - min + 1)) + min;
const num = RandomNum(1, 10); // 5

布尔技能

15、短路运算符

const a = d && 1; // Fake operation, judge from left to right, return a false value when encountering a false value, and no longer execute it later, otherwise return the last true value
const b = d || 1; // Take the true operation, judge from left to right, return the true value when encountering the true value, and do not execute it later, otherwise return the last false value
const c = !d; // Returns false if a single expression converts to true, otherwise returns true

16、确定数据类型

可确定的类型：undefined、null、string、number、boolean、array、object、symbol、date、regexp、function、asyncfunction、arguments、set、map、weakset、weakmap

function DataType(tgt, type) {
    const dataType = Object.prototype.toString.call(tgt).replace(/\[object (\w+)\]/, "$1").toLowerCase();
    return type ? dataType === type : dataType;
}
DataType("test"); // "string"
DataType(20220314); // "number"
DataType(true); // "boolean"
DataType([], "array"); // true
DataType({}, "array"); // false

17、检查数组是否为空

const arr = [];
const flag = Array.isArray(arr) && !arr.length;
// flag => true

18、满足条件时执行

const flagA = true; // Condition A
const flagB = false; // Condition B
(flagA || flagB) && Func(); // Execute when A or B is satisfied
(flagA || !flagB) && Func(); // Execute when A is satisfied or B is not satisfied
flagA && flagB && Func(); // Execute when both A and B are satisfied
flagA && !flagB && Func(); // Execute when A is satisfied and B is not satisfied

19、如果非假则执行

const flag = false; // undefined、null、""、0、false、NaN
!flag && Func();

20、数组不为空时执行

const arr = [0, 1, 2];
arr.length && Func();

21、对象不为空时执行

const obj = { a: 0, b: 1, c: 2 };
Object.keys(obj).length && Func();

阵列技能

22、克隆数组

const _arr = [0, 1, 2];
const arr = [..._arr];
// arr => [0, 1, 2]

23、合并数组

const arr1 = [0, 1, 2];
const arr2 = [3, 4, 5];
const arr = [...arr1, ...arr2];
// arr => [0, 1, 2, 3, 4, 5];

24、去重数组

const arr = [...new Set([0, 1, 1, null, null])];
// arr => [0, 1, null]

25、混淆数组

const arr = [0, 1, 2, 3, 4, 5].slice().sort(() => Math.random() - .5);
// arr => [3, 4, 0, 5, 1, 2]

26、清空数组

const arr = [0, 1, 2];
arr.length = 0;
// arr => []

27、截断数组

const arr = [0, 1, 2];
arr.length = 2;
// arr => [0, 1]

28、交换数值

let a = 0;
let b = 1;
[a, b] = [b, a];
// a b => 1 0

29、过滤空值

空值：undefined,null,””,0,false,NaN

const arr = [undefined, null, "", 0, false, NaN, 1, 2].filter(Boolean);
// arr => [1, 2]

30、在数组开头插入成员

let arr = [1, 2];
arr.unshift(0);
arr = [0].concat(arr);
arr = [0, ...arr];
// arr => [0, 1, 2]

31、在数组末尾插入元素

let arr = [0, 1]; 
arr.push(2);
arr.concat(2);
arr[arr.length] = 2;
arr = [...arr, 2];
// arr => [0, 1, 2]

32、计算数组成员的数量

const arr = [0, 1, 1, 2, 2, 2];
const count = arr.reduce((t, v) => {
 t[v] = t[v] ? ++t[v] : 1;
 return t;
}, {});
// count => { 0: 1, 1: 2, 2: 3 }

33、解构嵌套数组成员

const arr = [0, 1, [2, 3, [4, 5]]];
const [a, b, [c, d, [e, f]]] = arr;
// a b c d e f => 0 1 2 3 4 5

34、解构数组成员别名

const arr = [0, 1, 2];
const { 0: a, 1: b, 2: c } = arr;
// a b c => 0 1 2

35、解构数组成员默认值

const arr = [0, 1, 2];
const [a, b, c = 3, d = 4] = arr;
// a b c d => 0 1 2 4

36、获取随机数组成员

const arr = [0, 1, 2, 3, 4, 5];
const randomItem = arr[Math.floor(Math.random() * arr.length)];
// randomItem => 1

37、创建指定长度的数组

const arr = [...new Array(3).keys()];
// arr => [0, 1, 2]

38、创建一个指定长度和相等值的数组

const arr = new Array(3).fill(0);
// arr => [0, 0, 0]

对象技能

39、克隆对象

const _obj = { a: 0, b: 1, c: 2 };
const obj = { ..._obj };
const obj = JSON.parse(JSON.stringify(_obj));
// obj => { a: 0, b: 1, c: 2 }

40、合并对象

const obj1 = { a: 0, b: 1, c: 2 };
const obj2 = { c: 3, d: 4, e: 5 };
const obj = { ...obj1, ...obj2 };
// obj => { a: 0, b: 1, c: 3, d: 4, e: 5 }

41、对象变量属性

const flag = false;
const obj = {
    a: 0,
    b: 1,
    [flag ? "c" : "d"]: 2
};
// obj => { a: 0, b: 1, d: 2 }

42、创建一个纯空对象

const obj = Object.create(null);
Object.prototype.a = 0;
// obj => {}

43、删除对象无用属性

const obj = { a: 0, b: 1, c: 2 }; 
const { a, ...rest } = obj;
// rest => { b: 1, c: 2 }

44、解构对象属性嵌套

const obj = { a: 0, b: 1, c: { d: 2, e: 3 } };
const { c: { d, e } } = obj;
// d e => 2 3

45、解构对象属性别名

const obj = { a: 0, b: 1, c: 2 };
const { a, b: d, c: e } = obj;
// a d e => 0 1 2

46、解构对象属性默认值

const obj = { a: 0, b: 1, c: 2 };
const { a, b = 2, d = 3 } = obj;
// a b d => 0 1 3

函数技能

47、函数自执行

const Func = function() {}(); // Commonly used
(function() {})(); // Commonly used
(function() {}()); // Commonly used
[function() {}()];
+ function() {}();
- function() {}();
~ function() {}();
! function() {}();
new function() {};
new function() {}();
void function() {}();
typeof function() {}();
delete function() {}();
1, function() {}();
1 ^ function() {}();
1 > function() {}();

48、一次性函数

适合运行一些只需要执行一次的初始化代码。

function Func() {
    console.log("x");
    Func = function() {
        console.log("y");
    }
}

49、延迟加载函数

当函数中的复杂判断分支越来越多时，可以大大节省资源开销。

function Func() {
    if (a === b) {
        console.log("x");
    } else {
        console.log("y");
    }
}
// replace with
function Func() {
    if (a === b) {
        Func = function() {
            console.log("x");
        }
    } else {
        Func = function() {
            console.log("y");
        }
    }
    return Func();
}

50、检测非空参数

function IsRequired() {
    throw new Error("param is required");
}
function Func(name = IsRequired()) {
    console.log("I Love " + name);
}
Func(); // "param is required"
Func("You"); // "I Love You"

51、字符串创建函数

const Func = new Function("name", "console.log(\"I Love \" + name)");

52、优雅地处理错误信息

try {
    Func();
} catch (e) {
    location.href = "https://stackoverflow.com/search?q=[js]+" + e.message;
}

53、优雅地处理 Async/Await 参数

function AsyncTo(promise) {
    return promise.then(data => [null, data]).catch(err => [err]);
}
const [err, res] = await AsyncTo(Func());

54、优雅地处理多个函数返回值

function Func() {
    return Promise.all([
        fetch("/user"),
        fetch("/comment")
    ]);
}
const [user, comment] = await Func();

DOM 技能

55、显示所有 DOM 边框

[].forEach.call($$("*"), dom => {
    dom.style.outline = "1px solid #" + (~~(Math.random() * (1 << 24))).toString(16);
});

56、响应式页面

页面基于设计图但需要适配多个模型，元素大小使用rem设置。

function AutoResponse(width = 750) {
    const target = document.documentElement;
    target.clientWidth >= 600
        ? (target.style.fontSize = "80px")
        : (target.style.fontSize = target.clientWidth / width * 100 + "px");
}

57、过滤 XSS

function FilterXss(content) {
    let elem = document.createElement("div");
    elem.innerText = content;
    const result = elem.innerHTML;
    elem = null;
    return result;
}

58、访问本地存储

const love = JSON.parse(localStorage.getItem("love"));
localStorage.setItem("love", JSON.stringify("I Love You"));