JavaScript函数式工具库核心—Transducer、惰性求值与高性能数据处理|新宇宙博客返回列表函数式工具库核心
详解map/filter/reduce的函数式本质、数组方法链式优化问题、Transducer组合算法、惰性求值及memoize缓存策略
函数式工具库核心
函数式工具库（如 Lodash/fp、Ramda）的核心是一组经过精心设计的高阶函数。本文从零实现这些工具的核心，包括深克隆、深比较、去抖节流、惰性求值链等，并分析其在现代 JavaScript 开发中的取舍。
目录
- 集合操作工具
- 对象操作工具
- 函数控制工具
- 深比较与深克隆
- 惰性求值链
- 类型判断工具
- 实战案例
- 深度追问
- 总结表格
1. 集合操作工具
const _ = {
groupBy(arr, keyFn) {
return arr.reduce((groups, item) => {
const key = typeof keyFn === 'function' ? keyFn(item) : item[keyFn];
(groups[key] ||= []).push(item);
groups;
}, {});
},
() {
result = [];
( i = ; i < arr.; i += size) {
result.(arr.(i, i + size));
}
result;
},
() {
seen = ();
arr.( {
key = keyFn === ? (item) : item[keyFn];
(seen.(key)) ;
seen.(key);
;
});
},
() {
arr.( {
mapped = (item);
(.(mapped) && depth > ) {
acc.(....(mapped, x, depth - ));
} {
acc.(mapped);
}
acc;
}, []);
},
() {
(arrays. === ) [];
sets = arrays.( (a));
[...sets[]].( sets.( s.(item)));
},
() {
excludeSet = (excludes.());
arr.( !excludeSet.(item));
}
};
return
chunk
arr, size
const
for
let
0
length
push
slice
return
uniqBy
arr, keyFn
const
new
Set
return
filter
item =>
const
typeof
'function'
keyFn
if
has
return
false
add
return
true
flatMapDeep
arr, fn = x => x, depth = Infinity
return
reduce
(acc, item) =>
const
fn
if
Array
isArray
0
push
this
flatMapDeep
x =>
1
else
push
return
intersection
...arrays
if
length
0
return
const
map
a =>
new
Set
return
0
filter
item =>
every
s =>
has
difference
arr, ...excludes
const
new
Set
flat
return
filter
item =>
has
2. 对象操作工具
const objUtils = {
get(obj, path, defaultValue = undefined) {
const keys = Array.isArray(path) ? path : path.replace(/\[(\d+)\]/g, '.$1').split('.');
let result = obj;
for (const key of keys) {
result = result?.[key];
if (result === undefined) return defaultValue;
}
return result;
},
set(obj, path, value) {
const keys = Array.isArray(path) ? path : path.replace(/\[(\d+)\]/g, '.$1').split('.');
let current = obj;
for (let i = 0; i < keys.length - 1; i++) {
const key = keys[i];
const nextKey = keys[i + 1];
if (!(key in current) || typeof current[key] !== 'object') {
current[key] = /^\d+$/.test(nextKey) ? [] : {};
}
current = current[key];
}
current[keys[keys.length - 1]] = value;
return obj;
},
pick(obj, keys) {
return keys.reduce((result, key) => {
if (key in obj) result[key] = obj[key];
return result;
}, {});
},
omit(obj, keys) {
const keySet = new Set(keys);
return Object.fromEntries(Object.entries(obj).filter(([k]) => !keySet.has(k)));
},
merge(target, ...sources) {
for (const source of sources) {
for (const [key, value] of Object.entries(source)) {
if (value && typeof value === 'object' && !Array.isArray(value)) {
target[key] = this.merge(target[key] || {}, value);
} else {
target[key] = value;
}
}
}
return target;
}
};
const data = { user: { profile: { name: 'Alice', settings: { theme: 'dark' } } } };
console.log(objUtils.get(data, 'user.profile.name'));
console.log(objUtils.get(data, 'user.profile.missing', 'default'));
3. 函数控制工具
const fnUtils = {
debounce(fn, delay, { leading = false, trailing = true, maxWait } = {}) {
let timer, lastCallTime, lastInvokeTime = 0, result;
function invoke(time, args, thisArg) {
lastInvokeTime = time;
result = fn.apply(thisArg, args);
return result;
}
function debounced(...args) {
const now = Date.now();
const isInvoking = shouldInvoke(now);
lastCallTime = now;
if (isInvoking && leading && !timer) {
invoke(now, args, this);
}
clearTimeout(timer);
timer = setTimeout(() => {
timer = null;
if (trailing) invoke(Date.now(), args, this);
}, delay);
if (maxWait !== undefined) {
const timeSinceLastInvoke = now - lastInvokeTime;
if (timeSinceLastInvoke >= maxWait) {
invoke(now, args, this);
}
}
return result;
}
function shouldInvoke(time) {
return !lastCallTime || (time - lastCallTime >= delay);
}
debounced.cancel = () => { clearTimeout(timer); timer = null; };
debounced.flush = () => { if (timer) { clearTimeout(timer); timer = null; } };
return debounced;
},
throttle(fn, interval) {
return this.debounce(fn, interval, { leading: true, trailing: true, maxWait: interval });
},
memoize(fn, { maxSize = 100, ttl = 0, keyFn } = {}) {
const cache = new Map();
return function(...args) {
const key = keyFn ? keyFn(...args) : JSON.stringify(args);
if (cache.has(key)) {
const { value, timestamp } = cache.get(key);
if (!ttl || Date.now() - timestamp < ttl) {
return value;
}
cache.delete(key);
}
const value = fn.apply(this, args);
cache.set(key, { value, timestamp: Date.now() });
if (cache.size > maxSize) {
const firstKey = cache.keys().next().value;
cache.delete(firstKey);
}
return value;
};
}
};
4. 深比较与深克隆
function deepEqual(a, b, seen = new WeakSet()) {
if (Object.is(a, b)) return true;
if (typeof a !== 'object' || typeof b !== 'object') return false;
if (a === null || b === null) return false;
if (seen.has(a)) return true;
seen.add(a);
if (a instanceof Date && b instanceof Date) return a.getTime() === b.getTime();
if (a instanceof RegExp && b instanceof RegExp) return a.toString() === b.toString();
if (a instanceof Map && b instanceof Map) {
if (a.size !== b.size) return false;
for (const [key, val] of a) {
if (!b.has(key) || !deepEqual(val, b.get(key), seen)) return false;
}
return true;
}
if (a instanceof Set && b instanceof Set) {
if (a.size !== b.size) return false;
for (const val of a) { if (!b.has(val)) return false; }
return true;
}
const keysA = Object.keys(a);
const keysB = Object.keys(b);
if (keysA.length !== keysB.length) return false;
return keysA.every(key => deepEqual(a[key], b[key], seen));
}
function deepClone(obj, seen = new WeakMap()) {
if (obj === null || typeof obj !== 'object') return obj;
if (obj instanceof Date) return new Date(obj);
if (obj instanceof RegExp) return new RegExp(obj.source, obj.flags);
if (seen.has(obj)) return seen.get(obj);
const clone = Array.isArray(obj) ? [] : Object.create(Object.getPrototypeOf(obj));
seen.set(obj, clone);
if (obj instanceof Map) {
obj.forEach((val, key) => clone.set(deepClone(key, seen), deepClone(val, seen)));
return clone;
}
if (obj instanceof Set) {
obj.forEach(val => clone.add(deepClone(val, seen)));
return clone;
}
for (const key of Reflect.ownKeys(obj)) {
const descriptor = Object.getOwnPropertyDescriptor(obj, key);
if (descriptor.value !== undefined) {
descriptor.value = deepClone(descriptor.value, seen);
}
Object.defineProperty(clone, key, descriptor);
}
return clone;
}
5. 惰性求值链
class LazyChain {
#source;
#transforms = [];
constructor(source) {
this.#source = source;
}
map(fn) {
const chain = new LazyChain(this.#source);
chain.#transforms = [...this.#transforms, { type: 'map', fn }];
return chain;
}
filter(fn) {
const chain = new LazyChain(this.#source);
chain.#transforms = [...this.#transforms, { type: 'filter', fn }];
return chain;
}
take(n) {
const chain = new LazyChain(this.#source);
chain.#transforms = [...this.#transforms, { type: 'take', n }];
return chain;
}
value() {
const results = [];
let taken = Infinity;
for (const t of this.#transforms) {
if (t.type === 'take') taken = t.n;
}
for (const item of this.#source) {
let value = item;
let skip = false;
for (const transform of this.#transforms) {
if (transform.type === 'map') {
value = transform.fn(value);
} else if (transform.type === 'filter') {
if (!transform.fn(value)) { skip = true; break; }
} else if (transform.type === 'take') {
if (results.length >= transform.n) return results;
}
}
if (!skip) {
results.push(value);
if (results.length >= taken) break;
}
}
return results;
}
}
const result = new LazyChain([1,2,3,4,5,6,7,8,9,10])
.filter(n => n % 2 === 0)
.map(n => n * n)
.take(3)
.value();
console.log(result);
6. 类型判断工具
const TypeCheck = {
getType(value) {
return Object.prototype.toString.call(value).slice(8, -1);
},
isPlainObject(value) {
if (this.getType(value) !== 'Object') return false;
const proto = Object.getPrototypeOf(value);
return proto === null || proto === Object.prototype;
},
isEmpty(value) {
if (value == null) return true;
if (typeof value === 'string' || Array.isArray(value)) return value.length === 0;
if (value instanceof Map || value instanceof Set) return value.size === 0;
if (typeof value === 'object') return Object.keys(value).length === 0;
return false;
},
isNil: (v) => v === null || v === undefined,
isFunction: (v) => typeof v === 'function',
isPromise: (v) => v != null && typeof v.then === 'function',
isIterable: (v) => v != null && typeof v[Symbol.iterator] === 'function',
isAsyncIterable: (v) => v != null && typeof v[Symbol.asyncIterator] === 'function'
};
7. 实战案例
实战案例 1：配置系统
const defaultConfig = {
server: { port: 3000, host: 'localhost' },
database: { url: 'localhost:5432', pool: { min: 2, max: 10 } },
logging: { level: 'info', format: 'json' }
};
const envConfig = {
server: { port: process.env.PORT },
database: { url: process.env.DATABASE_URL }
};
const fileConfig = loadConfigFile('./config.yaml');
const config = objUtils.merge({}, defaultConfig, fileConfig, envConfig);
实战案例 2：数据处理管道
const processCSVData = pipe(
parseCSV,
rows => _.chunk(rows, 1000),
chunks => chunks.map(chunk =>
chunk
.filter(row => row.status === 'active')
.map(row => objUtils.pick(row, ['id', 'name', 'email']))
),
chunks => chunks.flat(),
rows => _.uniqBy(rows, 'email'),
rows => _.groupBy(rows, row => row.email.split('@')[1])
);
实战案例 3：表单状态管理
class FormState {
#initial;
#current;
#history = [];
constructor(initial) {
this.#initial = deepClone(initial);
this.#current = deepClone(initial);
}
set(path, value) {
this.#history.push(deepClone(this.#current));
objUtils.set(this.#current, path, value);
return this;
}
get(path) {
return objUtils.get(this.#current, path);
}
get isDirty() {
return !deepEqual(this.#initial, this.#current);
}
get changes() {
return diff(this.#initial, this.#current);
}
undo() {
if (this.#history.length > 0) {
this.#current = this.#history.pop();
}
return this;
}
reset() {
this.#current = deepClone(this.#initial);
this.#history = [];
return this;
}
}
8. 深度追问
Q1：Lodash 在 2024+ 还有必要吗？
原生 Array 方法已覆盖大部分需求。但 _.get、_.debounce、_.cloneDeep、_.merge 等在复杂应用中仍有价值。推荐按需引入（lodash-es/get），或使用 es-toolkit 等现代替代。
Q2：structuredClone 能否完全替代深克隆？
不能。structuredClone 不支持：函数、DOM 节点、Symbol 属性、原型链、属性描述符。它适合纯数据克隆，不适合复杂对象。
Q3：惰性求值的实际收益有多大？
在大数据集 + 多步转换 + take 限制的场景中，惰性求值可以减少 90%+ 的计算。但对于小数组（<100 项），惰性开销反而更大。
9. 总结表格
| 工具类别 | 典型函数 | 原生替代 |
|---|
| 集合操作 | groupBy, chunk, uniq | Object.groupBy (ES2024) |
| 对象操作 | get, set, merge | 可选链 ?., structuredClone |
| 函数控制 | debounce, throttle, once | 无原生替代 |
| 类型判断 | isPlainObject, isEmpty | typeof + instanceof |
| 深操作 | deepEqual, deepClone | structuredClone (部分) |
