更新 重构

软件工程/编码/代码重构.md

@@ -384,4 +384,174 @@ function foundPerson(people) {
 　const candidates = ["Don", "John", "Kent"];
 　return people.find(p => candidates.includes(p)) || '';
 }
-```
+```
+
+### 搬移特性
+
+- 搬移函数
+
+对于某函数，如果它频繁使用了其他上下文的元素，那么就考虑将它搬移到那个上下文里
+
+```js
+class Account {
+　get overdraftCharge() {...}
+}
+```
+
+↓
+
+```js
+class AccountType {
+    get overdraftCharge() {...}
+}
+```
+
+- 搬移字段
+
+![批注 2020-07-02 124318](/assets/批注%202020-07-02%20124318.png)
+
+对于早期设计不良的数据结构，使用此方法改造它
+
+```js
+class Customer {
+  get plan() {return this._plan;}
+  get discountRate() {return this._discountRate;}
+}
+```
+
+↓
+
+```js
+class Customer {
+  get plan() {return this._plan;}
+  get discountRate() {return this.plan.discountRate;}
+}
+```
+
+- 搬移语句到函数
+
+使用这个方法将分散的逻辑聚合到函数里面，方便理解修改
+
+```js
+result.push(`<p>title: ${person.photo.title}</p>`); 
+result.concat(photoData(person.photo));
+
+function photoData(aPhoto) { 
+　return [
+　　`<p>location: ${aPhoto.location}</p>`,
+　　`<p>date: ${aPhoto.date.toDateString()}</p>`,
+ ];
+}
+```
+
+↓
+
+```js
+result.concat(photoData(person.photo));
+
+function photoData(aPhoto) { 
+　return [
+　　`<p>title: ${aPhoto.title}</p>`,
+　　`<p>location: ${aPhoto.location}</p>`,
+　　`<p>date: ${aPhoto.date.toDateString()}</p>`,
+　];
+}
+```
+
+- 搬移语句到调用者
+
+上述的反向操作
+
+对于代码演进，函数某些代码职责发生变化，将它们移除出去
+
+- 以函数调用取代内联代码
+
+一些函数的函数名就拥有足够的表达能力
+
+```js
+let appliesToMass = false; 
+for(const s of states) {
+  if (s === "MA") appliesToMass = true;
+}
+```
+
+↓
+
+```js
+appliesToMass = states.includes("MA");
+```
+
+- 移动语句
+
+让存在关联的东西一起出现，可以使代码更容易理解
+
+```js
+const pricingPlan = retrievePricingPlan(); 
+const order = retreiveOrder();
+let charge;
+const chargePerUnit = pricingPlan.unit;
+```
+
+↓
+
+```js
+const pricingPlan = retrievePricingPlan(); 
+const chargePerUnit = pricingPlan.unit; 
+const order = retreiveOrder();
+let charge;
+```
+
+- 拆分循环
+
+对一个循环做了多件事的代码，拆分它，使各段代码职责更加明确
+
+虽然这样可能会对性能造成一些损失
+
+```js
+let averageAge = 0;
+let totalSalary = 0;
+for (const p of people) {
+　averageAge += p.age;
+　totalSalary += p.salary;
+}
+averageAge = averageAge / people.length;
+```
+
+↓
+
+```js
+let totalSalary = 0;
+for (const p of people) { 
+　totalSalary += p.salary;
+}
+
+let averageAge = 0;
+for (const p of people) {
+　averageAge += p.age;
+}
+averageAge = averageAge / people.length;
+```
+
+- 以管代取代循环
+
+一些逻辑如果采用管道编写，可读性会更强
+
+```js
+const names = [];
+for (const i of input) {
+  if (i.job === "programmer") 
+    names.push(i.name);
+}
+```
+
+↓
+
+```js
+const names = input
+  .filter(i => i.job === "programmer")
+  .map(i => i.name);
+```
+
+- 移除死代码
+
+移除那些永远不会允许的代码