每种语言都有自己的怪癖，最常用的编程语言JavaScript也不例外。本文将介绍大量的 JavaScript 速记优化技巧，这些技巧可以帮助您编写更好的代码，并确保这不是您遇到它们时的反应：

1. 多个字符串检查

通常，您可能需要检查 a 是否等于多个值之一，并且很快就会变得疲惫不堪。幸运的是，JavaScript 有一个内置的方法来帮助你解决这个问题。string

// Long-hand
const isVowel = (letter) => {
  if (
    letter === "a" ||
    letter === "e" ||
    letter === "i" ||
    letter === "o" ||
    letter === "u"
  ) {
    return true;
  }
  return false;
};

// Short-hand
const isVowel = (letter) =>
  ["a", "e", "i", "o", "u"].includes(letter);

2. 和循环For-ofFor-in

For-of循环是迭代 或 的好方法，而不必手动跟踪 的索引。For-inarrayobjectkeysobject

For-of

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

// Long-hand
for (let i = 0; i < arr.length; i++) {
  const element = arr[i];
  // ...
}

// Short-hand
for (const element of arr) {
  // ...
}

For-in

const obj = {
  a: 1,
  b: 2,
  c: 3,
};

// Long-hand
const keys = Object.keys(obj);
for (let i = 0; i < keys.length; i++) {
  const key = keys[i];
  const value = obj[key];
  // ...
}

// Short-hand
for (const key in obj) {
  const value = obj[key];
  // ...
}

3. 虚假支票

如果要检查变量是 、 、 、 还是空变量，则可以使用 Logical Not （） 运算符一次检查所有变量，而无需编写多个条件。这使得检查变量是否包含有效数据变得容易。nullundefined0falseNaNstring!

// Long-hand
const isFalsey = (value) => {
  if (
    value === null ||
    value === undefined ||
    value === 0 ||
    value === false ||
    value === NaN ||
    value === ""
  ) {
    return true;
  }
  return false;
};

// Short-hand
const isFalsey = (value) => !value;

4. 三元算子

作为 JavaScript 开发人员，您一定遇到过 .这是编写简洁语句的好方法。但是，您也可以使用它来编写简洁的代码，甚至将它们链接起来以检查多个条件。ternary operatorif-else

// Long-hand
let info;
if (value < minValue) {
  info = "Value is too small";
} else if (value > maxValue) {
  info = "Value is too large";
} else {
  info = "Value is in range";
}

// Short-hand
const info =
  value < minValue
    ? "Value is too small"
    : value > maxValue ? "Value is too large" : "Value is in range";

5. Function calls

With the help of the , you can also determine which function to call based on conditions.ternary operator

IMPORTANT SIDE-NOTE: The of the functions must be the same, else you risk running into an errorscall signature

function f1() {
  // ...
}
function f2() {
  // ...
}

// Long-hand
if (condition) {
  f1();
} else {
  f2();
}

// Short-hand
(condition ? f1 : f2)();

6. Switch shorthand

Long switch cases can often be optimized by using an object with the keys as the switches and the values as the return values.

const dayNumber = new Date().getDay();

// Long-hand
let day;
switch (dayNumber) {
  case 0:
    day = "Sunday";
    break;
  case 1:
    day = "Monday";
    break;
  case 2:
    day = "Tuesday";
    break;
  case 3:
    day = "Wednesday";
    break;
  case 4:
    day = "Thursday";
    break;
  case 5:
    day = "Friday";
    break;
  case 6:
    day = "Saturday";
}

// Short-hand
const days = {
  0: "Sunday",
  1: "Monday",
  2: "Tuesday",
  3: "Wednesday",
  4: "Thursday",
  5: "Friday",
  6: "Saturday",
};
const day = days[dayNumber];

7. 回退值

运算符可以为变量设置回退值。||

// Long-hand
let name;
if (user?.name) {
  name = user.name;
} else {
  name = "Anonymous";
}

// Short-hand
const name = user?.name || "Anonymous";

这就是所有人！