JavaScript系列（71）--函数式编程进阶详解

JavaScript函数式编程进阶详解 🎯

今天，让我们深入探讨JavaScript函数式编程的进阶内容。函数式编程是一种强大的编程范式，它通过使用纯函数和不可变数据来构建可预测和可维护的应用程序。

函数式编程进阶概念 🌟

💡 小知识：函数式编程的核心是通过函数组合来构建程序，避免状态共享和数据突变。高阶函数式编程更关注函数组合、柯里化、函子和monad等高级概念。

高级函数式特性实现 📊

// 1. 函数组合
const compose = (...fns) => x => fns.reduceRight((acc, fn) => fn(acc), x);const pipe = (...fns) => x => fns.reduce((acc, fn) => fn(acc), x);// 带错误处理的函数组合
const safeCompose = (...fns) => x => {try {return Either.right(fns.reduceRight((acc, fn) => fn(acc), x));} catch (error) {return Either.left(error);}
};// 2. 柯里化和偏函数应用
const curry = (fn) => {const arity = fn.length;return function curried(...args) {if (args.length >= arity) {return fn.apply(this, args);}return function(...moreArgs) {return curried.apply(this, args.concat(moreArgs));};};
};// 偏函数应用
const partial = (fn, ...presetArgs) => (...laterArgs) => fn(...presetArgs, ...laterArgs);// 3. 函子实现
class Functor {constructor(value) {this._value = value;}map(fn) {return new Functor(fn(this._value));}static of(value) {return new Functor(value);}
}// Maybe函子
class Maybe extends Functor {map(fn) {return this._value === null || this._value === undefined? Maybe.of(null): Maybe.of(fn(this._value));}getOrElse(defaultValue) {return this._value === null || this._value === undefined? defaultValue: this._value;}
}// Either函子
class Either {static left(value) {return new Left(value);}static right(value) {return new Right(value);}
}class Left extends Either {constructor(value) {super();this._value = value;}map() {return this;}getOrElse(defaultValue) {return defaultValue;}
}class Right extends Either {constructor(value) {super();this._value = value;}map(fn) {return Either.right(fn(this._value));}getOrElse() {return this._value;}
}

函数式数据结构 🚀

// 1. 不可变列表
class List {constructor(head, tail = null) {this.head = head;this.tail = tail;}static of(...items) {return items.reduceRight((acc, item) => new List(item, acc),null);}map(fn) {return new List(fn(this.head),this.tail ? this.tail.map(fn) : null);}filter(predicate) {if (!predicate(this.head)) {return this.tail ? this.tail.filter(predicate) : null;}return new List(this.head,this.tail ? this.tail.filter(predicate) : null);}reduce(fn, initial) {const result = fn(initial, this.head);return this.tail? this.tail.reduce(fn, result): result;}
}// 2. 不可变树
class Tree {constructor(value, left = null, right = null) {this.value = value;this.left = left;this.right = right;}map(fn) {return new Tree(fn(this.value),this.left ? this.left.map(fn) : null,this.right ? this.right.map(fn) : null);}fold(fn, initial) {const leftResult = this.left? this.left.fold(fn, initial): initial;const rightResult = this.right? this.right.fold(fn, leftResult): leftResult;return fn(rightResult, this.value);}
}// 3. 延迟求值序列
class LazySequence {constructor(generator) {this.generator = generator;}static of(...items) {return new LazySequence(function* () {yield* items;});}map(fn) {const self = this;return new LazySequence(function* () {for (const item of self.generator()) {yield fn(item);}});}filter(predicate) {const self = this;return new LazySequence(function* () {for (const item of self.generator()) {if (predicate(item)) {yield item;}}});}take(n) {const self = this;return new LazySequence(function* () {let count = 0;for (const item of self.generator()) {if (count >= n) break;yield item;count++;}});}toArray() {return [...this.generator()];}
}

性能优化实现 ⚡

// 1. 记忆化优化
const memoize = (fn) => {const cache = new Map();return (...args) => {const key = JSON.stringify(args);if (cache.has(key)) {return cache.get(key);}const result = fn(...args);cache.set(key, result);return result;};
};// 带有LRU缓存的记忆化
class LRUCache {constructor(maxSize) {this.maxSize = maxSize;this.cache = new Map();}get(key) {const item = this.cache.get(key);if (item) {// 更新访问顺序this.cache.delete(key);this.cache.set(key, item);}return item;}set(key, value) {if (this.cache.has(key)) {this.cache.delete(key);} else if (this.cache.size >= this.maxSize) {// 删除最久未使用的项const firstKey = this.cache.keys().next().value;this.cache.delete(firstKey);}this.cache.set(key, value);}
}// 2. 尾递归优化
const trampoline = fn => (...args) => {let result = fn(...args);while (typeof result === 'function') {result = result();}return result;
};// 3. 批处理优化
class BatchProcessor {constructor(batchSize = 1000) {this.batchSize = batchSize;this.batch = [];}add(item) {this.batch.push(item);if (this.batch.length >= this.batchSize) {this.process();}}process() {if (this.batch.length === 0) return;const result = this.batch.reduce((acc, item) => {// 处理逻辑return acc;}, []);this.batch = [];return result;}
}

最佳实践建议 💡

函数式设计模式

// 1. 命令模式的函数式实现
const createCommand = (execute, undo) => ({execute,undo
});const composeCommands = (...commands) => ({execute: () => commands.forEach(cmd => cmd.execute()),undo: () => commands.reverse().forEach(cmd => cmd.undo())
});// 2. 观察者模式的函数式实现
const createObservable = () => {const observers = new Set();return {subscribe: observer => {observers.add(observer);return () => observers.delete(observer);},notify: value => observers.forEach(observer => observer(value))};
};// 3. 策略模式的函数式实现
const strategies = new Map([['add', (a, b) => a + b],['subtract', (a, b) => a - b],['multiply', (a, b) => a * b],['divide', (a, b) => a / b]
]);const executeStrategy = (name, ...args) =>(strategies.get(name) || (() => null))(...args);