重构方法的速写

8/18/2025

《重构：改善既有代码的设计》中包含的重构方法速写

Written by: Lucas Liu on Mon Aug 18

第一组重构

1.1 提炼函数（Extract Function）

// before
function printOwing(invoice) {
    printBanner();
    let outstanding = calculateOutstanding(invoice);
    
    // print details
    console.log(`name: ${invoice.customer}`);
    console.log(`amount: ${outstanding}`);
}

// after
function printDetails(invoice) {
    printBanner();
    let outstanding = calculateOutstanding();
    printDetails(outstanding);

    function printDetails(outstanding) {
        console.log(`name: ${invoice.customer}`);
        console.log(`amount: ${outstanding}`);
    }
}

1.2 内联函数（Inline Function）

// before   
function getRating(driver) {
    return moreThanFiveLateDeliveries(driver) ? 2 : 1;
}

function moreThanFiveLateDeliveries(driver) {
    return driver.lateDeliveries > 5;
}

// after
function getRating(driver) {
    return (driver.lateDeliveries > 5) ? 2 : 1;
}

1.3 提炼变量（Extract Variable）

// before
function fn(order) {
    return order.quantity * order.itemPrice - Math.max(0, order.quantity - 500) * order.itemPrice * 0.05 + Math.min(order.quantity * order.itemPrice * 0.1, 100);
}

// after
function fn(order) {
    const basePrice = order.quantity * order.itemPrice;
    const quantityDiscount = Math.max(0, order.quantity - 500) * order.itemPrice * 0.05;
    const shipping = Math.min(order.quantity * order.itemPrice * 0.1, 100);
    return basePrice - quantityDiscount + shipping;
}

1.4 内联变量（Inline Variable）

// before
function fn(anOrder) {
    let basePrice = anOrder.basePrice;
    return (basePrice > 1000);
}

// after
function fn(anOrder) {
    return (anOrder.basePrice > 1000);
}

1.5 改变函数声明（Change Function Declaration）

// before
function circum(radius) { /* some code */ }

// after
function circumference(radius) { /* some code */ }

1.6 封装变量（Encapsulate Variable）

// before
let defaultOwner = { firstName: "martin", lastName: "Fowler" };

// after
let defaultOwnerData = {
    firstName: "martin",
    lastName: "Fowler"
};

export function defaultOwner() {
    return defaultOwnerData;
}

export function setDefaultOwner(arg) {
    defaultOwnerData = arg;
}

1.7 变量改名（Rename Variable）

// before
let a = height * width;

// after
let area = height * width;

1.8 引入参数对象（Introduce Parameter Object）

// before
function amountInvoiced(startDate, endDate) { /* some code */ }
function amountReceived(startDate, endDate) { /* some code */ }
function amountOverdue(startDate, endDate) { /* some code */ }

// after
function amountInvoiced(aDateRange) { /* some code */ }
function amountReceived(aDateRange) { /* some code */ }
function amountOverdue(aDateRange) { /* some code */ }

1.9 函数组合成类（Combine Functions into Class）

// before
function base(aReading) { /* some code */ }
function taxableCharge(aReading) { /* some code */ }
function calculateBaseCharge(aReading) { /* some code */ }

// after
class Reading {
    base() { /* some code */ }
    taxableCharge() { /* some code */ }
    calculateBaseCharge() { /* some code */ }
}

1.10 函数组合成变换（Combine Function into Transform）

// before
function base(aReading) { /* some code */ }
function taxableCharge(aReading) { /* some code */ }

// after
function enrichReading(argReading) {
    const aReading = _.cloneDeep(argReading);
    aReading.base = base(aReading);
    aReading.taxableCharge = taxableCharge(aReading);
    return aReading;
}

1.11 拆分阶段（Split Phase）

// before
const orderDate = orderString.split(/\s+/);
const productPrice = priceList[orderData[0].split("-")[1]];
const orderPrice = parseInt(orderData[1]) * productPrice;

// after
const orderRecord = parseOrder(order);
const orderPrice = price(orderRecord, priceList);

function parseOrder(aString) {
    const values = aString.split(/\s+/);
    return ({
        productID: values[0].split("-")[1],
        quantity: parseInt(values[1]),
    })
}

function price(order, priceList) {
    return order.quantity * priceList[order.productID];
}

封装

2.1 封装记录（Encapsulate Record）

// before
const organization = { name: "Acme Gooseberries", country: "GB" };

// after
class Organization {
    constructor(data) {
        this._name = data.name;
        this._country = data.country;
    }
    get name() { return this._name; }
    set name(arg) { this._name = arg; }
    get country() { return this._country; }
    set country(arg) { this._country = arg; }
}

2.2 封装集合（Encapsulate Collection）

// before
class Person {
    constructor() {
        this._courses = [];
    }
    get courses() { return this._courses; }
    set courses(aList) { this._courses = aList; }
}

// after
class Person {
    constructor() {
        this._courses = [];
    }
    get courses() { return this._courses.slice(); }
    addCourse(aCourse) { this._courses.push(aCourse); }
    removeCourse(aCourse) {
        const index = this._courses.indexOf(aCourse);
        if (index !== -1) this._courses.splice(index, 1);
    }
}

2.3 以对象取代基本类型（Replace Primitive with Object）

// before
orders.filter(o => "high" === o.priority || "rush" === o.priority);

// after
orders.filter(o => o.priority.higherThan(new Priority("normal")));

2.4 以查询取代临时变量（Replace Temp with Query）

// before
const basePrice = this._quantity * this._itemPrice;
if (basePrice > 1000) {
    return basePrice * 0.95;
} else {
    return basePrice * 0.98;
}

// after
get basePrice() {
    return this._quantity * this._itemPrice;
}

...

if (this.basePrice > 1000) {
    return this.basePrice * 0.95;
} else {
    return this.basePrice * 0.98;
}

2.5 提炼类（Extract Class）

// before
class Person {
    get officeAreaCode() {return this._officeAreaCode;}
    get officeNumber() {return this._officeNumber;}
}

// after
class Person {
    get officeAreaCode() {return this._telephoneNumber.areaCode;}
    get officeNumber() {return this._telephoneNumber.number;}
}
class TelephoneNumber {
    get areaCode() {return this._areaCode;}
    get number() {return this._number;}
}

2.6 内联类（Inline Class）

// before
class Person {
    get officeAreaCode() {return this._telephoneNumber.areaCode;}
    get officeNumber() {return this._telephoneNumber.number;}
}
class TelephoneNumber {
    get areaCode() {return this._areaCode;}
    get number() {return this._number;}
}

// after
class Person {
    get officeAreaCode() {return this._officeAreaCode;}
    get officeNumber() {return this._officeNumber;}
}

2.7 隐藏委托关系（Hide Delegate）

// before
manager = aPerson.department.manager;

// after
manager = aPerson.manager;

class Person {
    get manager() {
        return this.department.manager;
    }
}

2.8 移除中间人（Remove Middle Man）

// before
manager = aPerson.manager;

class Person {
    get manager() {
        return this.department.manager;
    }
}

// after
manager = aPerson.department.manager;

2.9 替换算法（Substitute Algorithm）

// before
function foundPerson(people) {
    for(let i = 0; i < people.length; i++) {
        if (people[i] === "Don") {
            return "Don";
        }
        if (people[i] === "John") {
            return "John";
        }
        if (people[i] === "Kent") {
            return "Kent";
        }
    }
    return "";
}

// after
function foundPerson(people) {
    const candidates = ["Don", "John", "Kent"];
    return people.find(p => candidates.includes(p)) || "";
}