Strategy Pattern

package.json

@@ -1,7 +1,9 @@
 {
   "name": "js-examples",
+  "type": "commonjs",
   "packageManager": "[email protected]",
   "dependencies": {
+    "ts-node": "^10.9.2",
     "typescript": "^5.6.3"
   }
 }

src/patterns/strategy/context.impl.ts

@@ -0,0 +1,13 @@
+import {IBaseDiscountStrategy, IStrategyContext} from "./interfaces";
+
+export class StrategyContext implements IStrategyContext{
+  private strategy: IBaseDiscountStrategy;
+
+  constructor(strategy: IBaseDiscountStrategy) {
+    this.strategy = strategy;
+  }
+
+  calculateFinalPrice(price: number): number {
+    return this.strategy.calculateDiscount(price);
+  }
+}

src/patterns/strategy/examples.ts

@@ -0,0 +1,20 @@
+import {StrategyContext, FixedDiscount, PercentageDiscount} from './'
+
+const RANDOM_FIXED_DISCOUNT = 500;
+const RANDOM_PERCENTAGE_DISCOUNT = 15;
+const RANDOM_PRICE = 1000;
+
+const fixed = new FixedDiscount(RANDOM_FIXED_DISCOUNT);
+const percentage = new PercentageDiscount(RANDOM_PERCENTAGE_DISCOUNT);
+
+export const calculateFinalPrice = (price: number, strategy: FixedDiscount | PercentageDiscount): number => {
+  const context = new StrategyContext(strategy);
+
+  const resultWithDiscount = context.calculateFinalPrice(price);
+
+  console.log({price, strategyName: strategy.name, result: resultWithDiscount});
+  return resultWithDiscount;
+};
+
+calculateFinalPrice(RANDOM_PRICE, fixed);
+calculateFinalPrice(RANDOM_PRICE, percentage);

src/patterns/strategy/index.ts

@@ -0,0 +1,3 @@
+export * from './interfaces'
+export * from './strategies.impl'
+export * from './context.impl'

src/patterns/strategy/interfaces.ts

@@ -0,0 +1,17 @@
+export interface IBaseDiscountStrategy {
+  name: string;
+  calculateDiscount(price: number): number;
+}
+
+export interface IFixedDiscountStrategy extends IBaseDiscountStrategy {
+  amount: number;
+}
+
+export interface IPercentageDiscountStrategy extends IBaseDiscountStrategy {
+  percentage: number;
+}
+
+export interface IStrategyContext {
+
+  calculateFinalPrice(price: number): number;
+}

src/patterns/strategy/strategies.impl.ts

@@ -0,0 +1,21 @@
+import {IFixedDiscountStrategy, IPercentageDiscountStrategy} from './interfaces';
+
+export class FixedDiscount implements IFixedDiscountStrategy {
+  public name = 'FixedDiscount';
+
+  constructor(public amount: number) {}
+
+  calculateDiscount(price: number): number {
+    return price - this.amount;
+  }
+}
+
+export class PercentageDiscount implements IPercentageDiscountStrategy {
+  public name = 'PercentageDiscount';
+
+  constructor(public percentage: number) {}
+
+  calculateDiscount(price: number): number {
+    return price - (price * this.percentage) / 100;
+  }
+}

src/patterns/strategy/strategy.md

@@ -0,0 +1,4 @@
+# "Strategy" Pattern Explanation:
+The Strategy pattern allows you to define a family of algorithms, encapsulate each one, and make them replaceable.
+It lets the algorithm vary independently of the clients that use it.
+A typical use case would be implementing different **sorting** or **pricing** strategies.

tsconfig.json

@@ -0,0 +1,18 @@
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+    "target": "es2020",
+    "module": "commonjs",
+    "rootDir": "./src",
+    "outDir": "./dist",
+    "strict": true,
+    "esModuleInterop": true,
+    "skipLibCheck": true,
+    "forceConsistentCasingInFileNames": true
+  },
+  "include": [
+    "src/**/**/*.ts"
+  ],
+  "exclude": [
+    "node_modules"
+  ]
+}

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