代码优化

1. 当同时声明多个变量时，可简写成一行

//常规
let x;
let y = 20;

//简写
let x,
  y = 20;

2. 使用三元(三目)运算符简化 if else

//常规
const x = 20;
let answer;

if (x > 10) {
  answer = "大于 10";
} else {
  answer = "小于 10";
}

//简写
const answer = x > 10 ? "大于 10" : "小于 10";

// 嵌套版
const answer = x > 10 ? "大于10" : x < 5 ? "小于5" : "在5和10之间";

3. 使用 || 运算符给变量指定默认值

本质是利用了 || 运算符的特点，表达式会依次进行布尔判定返回能确定结果的最后一个数据

//常规
let imagePath;

if (path !== null && path !== undefined && path !== "") {
  imagePath = getImagePath();
} else {
  imagePath = "default.jpg";
}

//简写
let imagePath = getImagePath() || "default.jpg";

4. 使用 && 运算符简化 if 语句

本质是利用了 && 运算符的特点，表达式会依次进行布尔判定返回能确定结果的最后一个数据

//常规
if (isLoggedin) {
  goToHomepage();
}

//简写
isLoggedin && goToHomepage();

5. 利用解构，可为多个变量同时赋值

//常规
let a, b, c;

a = 5;
b = 8;
c = 12;

//简写
let [a, b, c] = [5, 8, 12];

6. 使用解构交换两个变量的值

let x = "Hello",
  y = 55;

//常规
const temp = x;
x = y;
y = temp;

//简写
[x, y] = [y, x];

7. 适用箭头函数简化函数

//常规
function add(num1, num2) {
  return num1 + num2;
}

//简写
const add = (num1, num2) => num1 + num2;

需要注意箭头函数和普通函数的区别

8. 使用字符串模板简化代码

使用模板字符串代替原始的字符串拼接

//常规
console.log("You got a missed call from " + number + " at " + time);

//简写
console.log(`You got a missed call from ${number} at ${time}`);

多行字符串也可使用字符串模板简化

//常规
console.log(
  "JavaScript, often abbreviated as JS, is a\n" +
    "programming language that conforms to the \n" +
    "ECMAScript specification. JavaScript is high-level,\n" +
    "often just-in-time compiled, and multi-paradigm."
);

//简写
console.log(`JavaScript, often abbreviated as JS, is a
            programming language that conforms to the
            ECMAScript specification. JavaScript is high-level,
            often just-in-time compiled, and multi-paradigm.`);

9. 对于多值匹配，可将所有值放在数组中，通过数组方法来简写

//常规
if (value === 1 || value === "one" || value === 2 || value === "two") {
  // Execute some code
}

// 简写 1
if ([1, "one", 2, "two"].indexOf(value) >= 0) {
  // Execute some code
}

// 简写 2
if ([1, "one", 2, "two"].includes(value)) {
  // Execute some code
}

10. 巧用 ES6 对象字面量语法

let firstname = "Amitav";
let lastname = "Mishra";

//常规
let obj = {
  firstname: firstname,
  lastname: lastname,
};

//简写
let obj = {
  firstname,
  lastname,
};

11. 使用一元运算符简化字符串转数字

//常规
let total = parseInt("453");
let average = parseFloat("42.6");

//简写
let total = +"453";
let average = +"42.6";

12. 使用 repeat()方法简化重复一个字符串

//常规
let str = "";
for (let i = 0; i < 5; i++) {
  str += "Hello ";
}
console.log(str); // Hello Hello Hello Hello Hello

// 简写
"Hello ".repeat(5);

// 想跟你说100声抱歉！
"sorry\n".repeat(100);

13. 使用双星号代替 Math.pow()

//常规
const power = Math.pow(4, 3); // 64

// 简写
const power = 4 ** 3; // 64

14. 巧用扩展操作符（...）简化代码

简化数组合并

let arr1 = [20, 30];

//常规
let arr2 = arr1.concat([60, 80]); // [20, 30, 60, 80]

//简写
let arr2 = [...arr1, 60, 80]; // [20, 30, 60, 80]

单层对象的拷贝

let obj = {
  x: 20,
  y: {
    z: 30,
  },
};

//常规
const makeDeepClone = (obj) => {
  let newObject = {};
  Object.keys(obj).map((key) => {
    if (typeof obj[key] === "object") {
      newObject[key] = makeDeepClone(obj[key]);
    } else {
      newObject[key] = obj[key];
    }
  });

  return newObject;
};

const cloneObj = makeDeepClone(obj);

//简写
const cloneObj = JSON.parse(JSON.stringify(obj));

//简写 for single level object
let obj = {
  x: 20,
  y: "hello",
};
const cloneObj = {
  ...obj,
};

15. if 语句

//常规
if (likeJavaScript === true) {
  // Execute some code
}

// 简写
if (likeJavaScript) {
  // Execute some code
}

16. 寻找数组中的最大和最小值

// 简写
const arr = [2, 8, 15, 4];
Math.max(...arr); // 15
Math.min(...arr); // 2

17. 使用 for in 和 for of 来简化普通 for 循环

let arr = [10, 20, 30, 40];

//常规
for (let i = 0; i < arr.length; i++) {
  console.log(arr[i]);
}

//简写
//for of loop
for (const val of arr) {
  console.log(val);
}

//for in loop
for (const index in arr) {
  console.log(arr[index]);
}

18. 简化获取字符串中的某个字符

let str = "jscurious.com";

//常规
str.charAt(2); // c

//简写
str[2]; // c

19. 移除对象属性

let obj = {
  x: 45,
  y: 72,
  z: 68,
  p: 98,
};

// 常规
delete obj.x;
delete obj.p;
console.log(obj); // {y: 72, z: 68}

// 简写
let { x, p, ...newObj } = obj;
console.log(newObj); // {y: 72, z: 68}

20. 使用 arr.filter(Boolean)过滤掉数组成员的值 falsey

let arr = [12, null, 0, "xyz", null, -25, NaN, "", undefined, 0.5, false];

//常规
let filterArray = arr.filter(function (value) {
  if (value) return value;
});
// filterArray = [12, "xyz", -25, 0.5]

// 简写
let filterArray = arr.filter(Boolean);
// filterArray = [12, "xyz", -25, 0.5]

21. switch 简写

//常规
switch (a) {
  case "张三":
    return "age是12";
  case "李四":
    return "age是120";
}

// 简写
const map = {
  张三: "age12",
  李四: "age120",
};
console.log(map["张三"]);

22. 对象嵌套属性解构

//常规
const { info } = {
  name: "张三",
  age: 13,
  info: {
    dec: "描述1",
    info: "信息",
  },
};
console.log(info.dec); // 描述1

// 简写
const {
  info: { dec },
} = {
  name: "张三",
  age: 13,
  info: {
    dec: "描述1",
    info: "信息",
  },
};
console.log(dec); // 描述1

23. 取整

var a = ~~2.33;
var b = 2.33 | 0;
var c = 2.33 >> 0;