Javascripts 中的 if … else 用起来倒是很方便，但是看起来就不舒服了

if (true) {
}

if (true) {
}

if (true) {
  if (true) {
    if (true) {
    }
  } else {
  }
} else {
}

上面看起来很闹心吧，下面讲讲优化：

一、三元优化

if (ture) else可以用三元操作符来优化它：

// Bad 😥
if (true) {
  console.log("Congratutions!")
} else {
  console.warn("Oops, something went wrong!")
}

// Great 🥰
true 
  ? console.log("Congratutions")
  : console.warn("Oops, something went wrong!")

二、与优化

true的情况下才执行可以用与来进行优化：

if (true) {
  alert(1)
}

// is equals to:

true && alert(1)

三、提前返回

如果有多个判断，按照复杂程度，从上到下，提前返回。

function handleRequest(req) {
  if (req.code >= 500) {
    return "Server error";
  }
  if (req.code >= 404) {
    return "Cilent error";
  }
  return "Suceess";
}

四、类表格优化

下面是类似表格似的选择，通常会用 switch 来进行优化

// Bad 😥
const weekday = (num) => {
  if (num === 1) {
    return "Monday"
  } else if (num === 2) {
    return "Tuesday"
  } else if (num === 3) {
    return "Wednesday"
  } else if (num === 4) {
    return "Thursday"
  } else if (num === 5) {
    return "Friday"
  } else if (num === 6) {
    return "Saturday"
  } else if (num === 7) {
    return "Sunday"
  } else {
    return "Unknown"
  }
}

console.log(weekday(1)) // Monday

switch 也不是最优解，用对象的键值对来解：

const weekday = (option) => {
    let obj = {
        1: "Monday",
        2: "Tuesday",
        3: "Wednesday",
        4: "Thursday",
        5: "Friday",
        6: "Saturday",
        0: "Sunday"
    }
    return obj[option] ?? "Unknown"
}

console.log(weekday(1)) // Monday

也可以用 ES6 的 map 来实现：

// Great 🥰
const weekday = (num) => {
  const map = new Map()
    .set(1, "Monday")
    .set(2, "Tuesday")
    .set(3, "Wednesday")
    .set(4, "Thursday")
    .set(5, "Friday")
    .set(6, "Saturday")
    .set(7, "Sunday");
  return map.has(num) ? map.get(num) : "Unknown";
};

console.log(weekday(1));

五、选项多对一的数组优化

看如下代码，多个选项对应一个返回：

const getContinent = (option) => {
  if (option === "China" || option === "Japan") {
    return "Asia";
  }
  if (option === "Germany" || option === "France") {
    return "Europe";
  }
};

console.log(getContinent("China"));

使用数组来容纳多个选项，然后用 includes 来判断并返回

const getContinent = (option) => {
  const Asia = ["China", "Japan"];
  const Europe = ["Germany", "Franch"];
  if (Asia.includes(option)) return "Asia";
  if (Europe.includes(option)) return "Europe";
  return "Unknown";
};

console.log(getContinent("China")); // Asia

进一步优化，用 && 与优化

const getContinent = (option) => {
  let [result, setResult] = ["unknown", (str) => (result = str)];
  const Asia = ["China", "Japan"];
  const Europe = ["Germany", "Franch"];
  Asia.includes(option) && setResult("Asia");
  Europe.includes(option) && setResult("Europe");
  return result;
};

console.log(getContinent("China"));