靈活運用JavaScript開發技巧

 

時間對比：時間個位數形式需補0

const time1 = "2019-03-31 21:00:00";const time2 = "2019-05-01 09:00:00";
const overtime = time1 > time2;
// overtime => false

 

格式化金錢

const ThousandNum = num => num.toString().replace(/\B(?=(\d{3})+(?!\d))/g, ",");
const money = ThousandNum(19941112);
// money => "19,941,112"

 

生成隨機ID

const RandomId = len =>Math.random().toString(36).substr(3, len);
const id = RandomId(10);
// id => "jg7zpgiqva"

 

生成隨機HEX色值

const RandomColor = () =>"#" + Math.floor(Math.random() * 0xffffff).toString(16).padEnd(6, "0");
const color = RandomColor();
// color => "#f03665"

 

生成星級評分

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

 

操做URL查詢參數

const params = new URLSearchParams(location.search.replace(/\?/ig, ""));
 // location.search = "?name=yajun&sex=female"params.has("yajun");
 // trueparams.get("sex");

 

Number Skill

取整：代替正數的Math.floor()，代替負數的Math.ceil()

const num1 = ~~ 1.69;const num2 = 1.69 | 0;
const num3 = 1.69 >> 0;
// num1 num2 num3 => 1 1 1

 

補零

const FillZero = (num, len) => num.toString().padStart(len, "0");
const num = FillZero(169, 5);
// num => "00169"

 

轉數值：只對null、""、false、數值字符串有效

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

 

時間戳

const timestamp = +newDate("2019-03-31");
// timestamp => 1553990400000

 

精確小數

const RoundNum = (num, decimal) =>Math.round(num * 10 ** decimal) / 10 ** decimal;
const num = RoundNum(1.69, 1);
// num => 1.7

 

判斷奇偶

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

 

取最小最大值

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

 

生成範圍隨機數

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

 

Boolean Skill

 

短路運算符

const a = d && 1; // 知足條件賦值：取假運算，從左到右依次判斷，遇到假值返回假值，後面再也不執行，不然返回最後一個真值const b = d || 1; // 默認賦值：取真運算，從左到右依次判斷，遇到真值返回真值，後面再也不執行，不然返回最後一個假值const c = !d; // 取假賦值：單個表達式轉換爲true則返回false，不然返回true複製代碼

 

判斷數據類型：undefined、null、string、number、boolean、array、object、symbol、date、regexp、function、asyncfunction、arguments、set、map、weakset、weakmap

functionDataType(tgt, type) { 
  const dataType = Object.prototype.toString.call(tgt).replace(/\[object /g, "").replace(/\]/g, "").toLowerCase(); 
return type ? dataType === type : dataType;}DataType("yajun"); 

// "string"DataType(19941112); 
// "number"DataType(true); 
// "boolean"DataType([], "array");
// trueDataType({}, "array"); 
// false

 

是否爲空數組

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

 

是否爲空對象

const obj = {};
const flag = DataType(obj, "object") && !Object.keys(obj).length;
// flag => true

 

知足條件時執行

const flagA = true; 
// 條件Aconst flagB = false; 
// 條件B(flagA || flagB) && Func(); 
// 知足A或B時執行(flagA || !flagB) && Func(); 
// 知足A或不知足B時執行flagA && flagB && Func(); 
// 同時知足A和B時執行flagA && !flagB && Func(); 
// 知足A且不知足B時執行

 

爲非假值時執行

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

 

數組不爲空時執行

const arr = [0, 1, 2];

arr.length && Func();

 

對象不爲空時執行

const obj = { a: 0, b: 1, c: 2 };

Object.keys(obj).length && Func();

 

函數退出代替條件分支退出

if (flag) { Func(); returnfalse;}// 換成if (flag) { return Func();}

 

switch/case使用區間

const age = 26;

switch (true) { caseisNaN(age): console.log("not a number");

break; case (age < 18): console.log("under age");

break; case (age >= 18): console.log("adult"); break;

default: console.log("please set your age"); break;}

 

Array Skill

 

克隆數組

const _arr = [0, 1, 2];

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

 

合併數組

const arr1 = [0, 1, 2];

const arr2 = [3, 4, 5];

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

 

去重數組

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

// arr => [0, 1, null]

 

混淆數組

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

// arr => [3, 4, 0, 5, 1, 2]

 

清空數組

const arr = [0, 1, 2];

arr.length = 0;// arr => []

 

截斷數組

const arr = [0, 1, 2];

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

 

交換賦值

let a = 0;

let b = 1;

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

 

過濾空值：undefined、null、""、0、false、NaN

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

// arr => [1, 2]

 

異步累計

asyncfunctionFunc(deps) { return deps.reduce(async(t, v) => { const dep = await t;

const version = await Todo(v);

dep[v] = version; return dep; }, Promise.resolve({}));}

const result = await Func(); // 需在async包圍下使用

 

數組首部插入成員

let arr = [1, 2]; // 如下方法任選一種arr.unshift(0);

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

 

數組尾部插入成員

let arr = [0, 1]; // 如下方法任選一種arr.push(2);

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

 

統計數組成員個數

const arr = [0, 1, 1, 2, 2, 2];const count = arr.reduce((t, c) => { t[c] = t[c] ? ++ t[c] : 1;

return t;}, {});// count => { 0: 1, 1: 2, 2: 3 }

 

解構數組成員嵌套

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

 

解構數組成員別名

const arr = [0, 1, 2];

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

 

解構數組成員默認值

const arr = [0, 1, 2];

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

 

獲取隨機數組成員

const arr = [0, 1, 2, 3, 4, 5];

const randomItem = arr[Math.floor(Math.random() * arr.length)];// randomItem => 1

 

建立指定長度數組

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

 

建立指定長度且值相等的數組

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

 

reduce代替map和filter

const _arr = [0, 1, 2];// mapconst arr = _arr.map(v => v * 2);const arr = _arr.reduce((t, c) => { t.push(c * 2); return t;}, []);// arr => [0, 2, 4]// filterconst arr = _arr.filter(v => v > 0);const arr = _arr.reduce((t, c) => { c > 0 && t.push(c); return t;}, []);// arr => [1, 2]// map和filterconst arr = _arr.map(v => v * 2).filter(v => v > 2);const arr = _arr.reduce((t, c) => { c = c * 2; c > 2 && t.push(c); return t;}, []);// arr => [4]

 

Object Skill

 

克隆對象

const _obj = { a: 0, b: 1, c: 2 }; // 如下方法任選一種const obj = { ..._obj };const obj = JSON.parse(JSON.stringify(_obj));// obj => { a: 0, b: 1, c: 2 }

 

合併對象

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 }

 

對象字面量：獲取環境變量時必用此方法，用它一直爽，一直用它一直爽

const env = "prod";const link = { dev: "Development Address", test: "Testing Address", prod: "Production Address"}[env];// link => "Production Address"

 

對象變量屬性

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

 

建立純空對象

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

 

刪除對象無用屬性

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

 

解構對象屬性嵌套

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

 

解構對象屬性別名

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

 

解構對象屬性默認值

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

 

Function Skill

 

函數自執行

const Func = function() {}(); // 經常使用(function() {})(); // 經常使用(function() {}()); // 經常使用[function() {}()];+ function() {}();- function() {}();~ function() {}();! function() {}();newfunction() {};newfunction() {}();voidfunction() {}();typeoffunction() {}();deletefunction() {}();1, function() {}();1 ^ function() {}();1 > function() {}();

 

隱式返回值：只能用於單語句返回值箭頭函數，若是返回值是對象必須使用()包住

const Func = function(name) { return"I Love " + name;};// 換成const Func = name =>"I Love " + name;

 

一次性函數：適用於運行一些只需執行一次的初始化代碼

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

 

惰性載入函數：函數內判斷分支較多較複雜時可大大節約資源開銷

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

 

檢測非空參數

functionIsRequired() { thrownewError("param is required");}functionFunc(name = IsRequired()) { console.log("I Love " + name);}Func(); // "param is required"Func("雅君妹紙"); // "I Love 雅君妹紙"

 

字符串建立函數

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

 

優雅處理錯誤信息

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

 

優雅處理Async/Await參數

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

 

優雅處理多個函數返回值

functionFunc() { returnPromise.all([ fetch("/user"), fetch("/comment") ]);}const [user, comment] = await Func(); // 需在async包圍下使用複製代碼

 

DOM Skill

 

顯示所有DOM邊框：調試頁面元素邊界時使用

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

 

自適應頁面：頁面基於一張設計圖但需作多款機型自適應，元素尺寸使用rem進行設置

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

 

過濾XSS

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

 

存取LocalStorage：反序列化取，序列化存

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