整潔的代碼不僅僅是讓人看起來舒服，更重要的是遵循一些規範能夠讓你的代碼更容易維護，同時降低bug機率。
1. 用命名的變量代替數組下標
// bad
const address = "One Infinite Loop, Cupertino 95014";
const cityZipCodeRegex = /^[^,\\]+[,\\\s]+(.+?)\s*(\d{5})?$/;
saveCityZipCode(
// 下標1,2不易於理解
address.match(cityZipCodeRegex)[1],
address.match(cityZipCodeRegex)[2]
);
// good
const address = "One Infinite Loop, Cupertino 95014";
const cityZipCodeRegex = /^[^,\\]+[,\\\s]+(.+?)\s*(\d{5})?$/;
// 使用數組解構更好的命名變量
const [, city, zipCode] = address.match(cityZipCodeRegex) || [];
saveCityZipCode(city, zipCode);
2. 函數的參數最好<=2個，儘量避免3個。
如果有很多參數就利用object傳遞，並使用解構。
3. 一個函數只做一件事。
好處在於compose, test, and reason about。
4. 不要自行擴展原型
如果想擴展原型，可以先繼承再添加方法，防止污染。
// bad
Array.prototype.diff = function diff(comparisonArray) {
const hash = new Set(comparisonArray);
return this.filter(elem => !hash.has(elem));
};
// good
class SuperArray extends Array {
diff(comparisonArray) {
const hash = new Set(comparisonArray);
return this.filter(elem => !hash.has(elem));
}
}
5. 用多態來代替條件語句
// bad
if (type === 'text') {
// do something
} else if (type === 'select') {
// do something else
}
個人寫這種代碼的一種常用方式是：
const control = {
text: {
mapper() {},
restore(){},
name: 'this is a text field',
},
select: {
mapper() {},
restore(){},
name: 'this is a select field',
}
}
control[type].mapper();
實際上就是多態（polymorphism），也可以考慮用class的方式，大概這樣：自己是個做了幾年軟件開發的老碼農，如果你對前端開發這門技術感興趣，我們的前端開發學習扣qun：767-273-102 從最基礎的HTML+CSS+JavaScript。jQuery，Ajax，node，angular等到移動端HTML5的項目實戰的資料都有整理，送給每一位學習前端的小夥伴
class Field {
...
}
class TextField extends Field {
mapper(){}
restore(){}
name = 'this is a text field';
}
class SelectField extends Field {
mapper(){}
restore(){}
name = 'this i```s a select field';
}
- 使用getter和setter函數。
// bad
function makeBankAccount() {
// ...
return {
balance: 0
// ...
};
}
const account = makeBankAccount();
account.balance = 100;
// good
function makeBankAccount() {
// this one is private
let balance = 0;
// a "getter", made public via the returned object below
function getBalance() {
return balance;
}
// a "setter", made public via the returned object below
function setBalance(amount) {
// ... validate before updating the balance
balance = amount;
}
return {
// ...
getBalance,
setBalance
};
}
const account = makeBankAccount();
account.setBalance(100);
你可以在getter和setter裏面做很多事情而不需要修改每一個.balance的地方。
7. Prefer composition over inheritance
儘量用組合來代替繼承，什麼情況下用繼承：
Your inheritance represents an “is-a” relationship and not a “has-a” relationship (Human->Animal vs. User->UserDetails).
You can reuse code from the base classes (Humans can move like all animals).
You want to make global changes to derived classes by changing a base class. (Change the caloric expenditure of all animals when they move).
8. SOLID
Single Responsibility Principle 單一職責原則
There should never be more than one reason for a class to change，一個類被改變的原因數量應該儘可能降低。如果一個類中功能太多，當你修改其中一點時會無法估量任何引用該類的模塊所受到的影響。
Open/Closed Principle 開放封閉原則
用戶可以在不修改內部實現的前提下自行擴展功能。例如有一個Http模塊，內部會根據環境判斷用哪個adaptor。如果用戶要添加adaptor就必須修改Http模塊。
// bad
class AjaxAdapter extends Adapter {
constructor() {
super();
this.name = "ajaxAdapter";
}
}
class NodeAdapter extends Adapter {
constructor() {
super();
this.name = "nodeAdapter";
}
}
class HttpRequester {
constructor(adapter) {
this.adapter = adapter;
}
fetch(url) {
if (this.adapter.name === "ajaxAdapter") {
return makeAjaxCall(url).then(response => {
// transform response and return
});
} else if (this.adapter.name === "nodeAdapter") {
return makeHttpCall(url).then(response => {
// transform response and return
});
}
}
}
function makeAjaxCall(url) {
// request and return promise
}
function makeHttpCall(url) {
// request and return promise
}
// good
class AjaxAdapter extends Adapter {
constructor() {
super();
this.name = "ajaxAdapter";
}
request(url) {
// request and return promise
}
}
class NodeAdapter extends Adapter {
constructor() {
super();
this.name = "nodeAdapter";
}
request(url) {
// request and return promise
}
}
class HttpRequester {
constructor(adapter) {
this.adapter = adapter;
}
fetch(url) {
return this.adapter.request(url).then(response => {
// transform response and return
});
}
}
Liskov Substitution Principle 裏式替換原則
父類和子類應該可以被交換使用而不會出錯。
// bad
class Rectangle {
constructor() {
this.width = 0;
this.height = 0;
}
setColor(color) {
// ...
}
render(area) {
// ...
}
setWidth(width) {
this.width = width;
}
setHeight(height) {
this.height = height;
}
getArea() {
return this.width * this.height;
}
}
class Square extends Rectangle {
setWidth(width) {
this.width = width;
this.height = width;
}
setHeight(height) {
this.width = height;
this.height = height;
}
}
function renderLargeRectangles(rectangles) {
rectangles.forEach(rectangle => {
rectangle.setWidth(4);
rectangle.setHeight(5);
const area = rectangle.getArea(); // BAD: Returns 25 for Square. Should be 20.
rectangle.render(area);
});
}
const rectangles = [new Rectangle(), new Rectangle(), new Square()];
renderLargeRectangles(rectangles);
上面的Rectangle不能直接替換Square，因爲會導致計算面積錯誤，考慮將計算面積的方法抽象出來：
class Shape {
setColor(color) {
// ...
}
render(area) {
// ...
}
}
class Rectangle extends Shape {
constructor(width, height) {
super();
this.width = width;
this.height = height;
}
getArea() {
return this.width * this.height;
}
}
class Square extends Shape {
constructor(length) {
super();
this.length = length;
}
getArea() {
return this.length * this.length;
}
}
function renderLargeShapes(shapes) {
shapes.forEach(shape => {
const area = shape.getArea();
shape.render(area);
});
}
const shapes = [new Rectangle(4, 5), new Rectangle(4, 5), new Square(5)];
renderLargeShapes(shapes);
Interface Segregation Principle 接口隔離原則
Clients should not be forced to depend upon interfaces that they do not use。舉例來說，一個功能模塊需要設計必須傳的參數和可選參數，不應該強迫用戶使用可選參數。
Dependency Inversion Principle 依賴注入原則
// bad
class InventoryRequester {
constructor() {
this.REQ_METHODS = ["HTTP"];
}
requestItem(item) {
// ...
}
}
class InventoryTracker {
constructor(items) {
this.items = items;
// BAD: We have created a dependency on a specific request implementation.
// We should just have requestItems depend on a request method: `request`
this.requester = new InventoryRequester();
}
requestItems() {
this.items.forEach(item => {
this.requester.requestItem(item);
});
}
}
const inventoryTracker = new InventoryTracker(["apples", "bananas"]);
inventoryTracker.requestItems();
上面例子在於，InventoryTracker內部實例化了InventoryRequester，也就意味着high-level的模塊需要知道low-level模塊的細節（比如實例化InventoryRequester需要知道它的構造參數等，或者說需要import該模塊，造成耦合）。
// good
class InventoryTracker {
constructor(items, requester) {
this.items = items;
this.requester = requester;
}
requestItems() {
this.items.forEach(item => {
this.requester.requestItem(item);
});
}
}
class InventoryRequesterV1 {
constructor() {
this.REQ_METHODS = ["HTTP"];
}
requestItem(item) {
// ...
}
}
class InventoryRequesterV2 {
constructor() {
this.REQ_METHODS = ["WS"];
}
requestItem(item) {
// ...
}
}
// By constructing our dependencies externally and injecting them, we can easily
// substitute our request module for a fancy new one that uses WebSockets.
const inventoryTracker = new InventoryTracker(
["apples", "bananas"],
new InventoryRequesterV2()
);
inventoryTracker.requestItems();
直接傳入low-level的實例而不需要考慮它是如何被實例化的，high-level只需要依賴抽象的接口就可以完成對子模塊的調用。
9. 註釋
Comments are an apology, not a requirement. Good code mostly documents itself. 好的代碼是自解釋的。
你會經常地遇到 bug 和其它一些問題。這可能會讓人沮喪，但你要儘量保持冷靜，並系統地去思考。記住實踐是解決問題的最佳方法。
