// bad (albeit way faster)
const arr = [1, 2, 3, 4];
const len = arr.length;
var i = -1;
var result = [];
while (++i < len) {
var n = arr[i];
if (n % 2 > 0) continue;
result.push(n * n);
}
// good
const arr = [1, 2, 3, 4];
const isEven = n => n % 2 == 0;
const square = n => n * n;
const result = arr.filter(isEven).map(square);
// bad
if (x === undefined || x === null) { ... }
// good
if (x == undefined) { ... }
循环
当你不得已使用可变的对象时最好不要使用循环，使用array.prototype的方法。
// bad
const sum = arr => {
var sum = 0;
var i = -1;
for (;arr[++i];) {
sum += arr[i];
}
return sum;
};
sum([1, 2, 3]); // => 6
// good
const sum = arr =>
arr.reduce((x, y) => x + y);
sum([1, 2, 3]); // => 6
如果你不想，或者说使用 array.prototype方法很恶心，建议使用递归
// bad
const createDivs = howMany => {
while (howMany--) {
document.body.insertAdjacentHTML("beforeend", "");
}
};
createDivs(5);
// bad
const createDivs = howMany =>
[...Array(howMany)].forEach(() =>
document.body.insertAdjacentHTML("beforeend", "")
);
createDivs(5);
// good
const createDivs = howMany => {
if (!howMany) return;
document.body.insertAdjacentHTML("beforeend", "");
return createDivs(howMany - 1);
};
createDivs(5);
// bad
var me = new Map();
me.set("name", "Ben").set("country", "Belgium");
// good
const me = new Map();
me.set("name", "Ben").set("country", "Belgium");
条件
建议用 匿名执行函数返回语句 代替 if,else,switch 语句。
// bad
var grade;
if (result < 50)
grade = "bad";
else if (result < 90)
grade = "good";
else
grade = "excellent";
// good
const grade = (() => {
if (result < 50)
return "bad";
if (result < 90)
return "good";
return "excellent";
})();
对象迭代
尽可能的避免使用 for .. in
const shared = { foo: "foo" };
const obj = Object.create(shared, {
bar: {
value: "bar",
enumerable: true
}
});
// bad
for (var prop in obj) {
if (obj.hasOwnProperty(prop))
console.log(prop);
}
// good
Object.keys(obj).forEach(prop => console.log(prop));
使用 Map 创建对象
在使用对象的时候，Map 是个更好的选择
// bad
const me = {
name: "Ben",
age: 30
};
var meSize = Object.keys(me).length;
meSize; // => 2
me.country = "Belgium";
meSize++;
meSize; // => 3
// good
const me = new Map();
me.set("name", "Ben");
me.set("age", 30);
me.size; // => 2
me.set("country", "Belgium");
me.size; // => 3
柯里化
柯里化很强大，但是很多开发者不是很熟悉。不要滥用它，但适当的使用是很不错的。
// bad
const sum = a => b => a + b;
sum(5)(3); // => 8
// good
const sum = (a, b) => a + b;
sum(5, 3); // => 8
可读性
不要用一些看似聪明的小技巧混淆代码的可读性
// bad
foo || doSomething();
// good
if (!foo) doSomething();
// bad
void function() { /* IIFE */ }();
// good
(function() { /* IIFE */ }());
// bad
const n = ~~3.14;
// good
const n = Math.floor(3.14);
代码复用
不要害怕创造许多小的，高度组合可重复使用的函数
// bad
arr[arr.length - 1];
// good
const first = arr => arr[0];
const last = arr => first(arr.slice(-1));
last(arr);
// bad
const product = (a, b) => a * b;
const triple = n => n * 3;
// good
const product = (a, b) => a * b;
const triple = product.bind(null, 3);
