您可以在 repo github 上找到这篇文章中的所有代码。
功能相关的挑战
参数和参数
/** * @param {function} fn * @return {number} */function functionlength(fn) { return fn.length;}// usage examplefunction myfunction(a, b, c) { console.log(a, b, c);}console.log(functionlength(myfunction)); // => 3/** * @param {...any} args * @return {number} */function numofarguments(...args) { // return args.length; return arguments.length;}// usage exampleconsole.log(numofarguments(1, 2, 3, 4, 5)); // => 5console.log(numofarguments()); // => 0
撰写
/** * @param {...functions} fns * @return function */function compose(...fns) { return function (x) { let result = x; for (const fn of fns.reverse()) { result = fn(result); } return result; };}// usage exampleconst add1 = (num) => num + 1;const double = (num) => num * 2;const subtract10 = (num) => num - 10;const composedfn = compose(subtract10, double, add1);console.log(composedfn(3)); // (3 + 1) * 2 - 10 => -2
柯里化
/** * @param {function} fn * @return {function} */function curry(fn) { return function curried(...args) { if (args.length >= fn.length) { return fn.apply(this, args); } return curried.bind(this, ...args); };}// usage example// single parameter casefunction add(a, b) { return a + b;}const curriedadd = curry(add);console.log(curriedadd(3)(4)); // => 7const alreadyaddedthree = curriedadd(3);console.log(alreadyaddedthree(4)); // => 7// fixed parameters casefunction addtwo(a, b) { return a + b;}const curriedaddtwo = curry(addtwo);console.log(curriedaddtwo(3, 4)); // => 7console.log(curriedaddtwo(3)(4)); // => 7const alreadyaddedthreeb = curriedadd(3);console.log(alreadyaddedthreeb(4)); // => 7//-------------------------------------------/** * @param {function} fn * @return {function} */function curry(fn) { return function curried(...args) { const bindfn = curried.bind(this, ...args); bindfn[symbol.toprimitive] = () => fn.call(this, ...args); return bindfn; };}// usage example// non-fixed parameters casefunction multiply(...numbers) { return numbers.reduce((a, b) => a * b, 1);}const curriedmultiply = curry(multiply);const multiplybythree = curriedmultiply(3);console.log(multiplybythree); // => 3console.log(multiplybythree(4)); // => 12const multiplybyfifteen = multiplybythree(5);console.log(multiplybyfifteen); // => 15console.log(multiplybyfifteen(2)); // => 30console.log(curriedmultiply(1)(2)(3)(4)); // => 24console.log(curriedmultiply(1, 2, 3, 4)); // => 24
备忘录
/** * @param {function} func * @return {function} */function memoize(fn) { const cache = new map(); return function (arg) { if (cache.has(arg)) { return cache.get(arg); } const result = fn.call(this, arg); cache.set(arg, result); return result; };}// usage examplefunction expensivefunction(n) { console.log("computing..."); return n * 2;}// create a memoized version of the function.const memoizedexpensivefunction = memoize(expensivefunction);// first call (computes and caches the result).console.log(memoizedexpensivefunction(5)); // => computing... 10// second call with the same argument (returns the cached result).console.log(memoizedexpensivefunction(5)); // => 10// third call with a different argument (computes and caches the new result).console.log(memoizedexpensivefunction(10)); // => computing... 20// fourth call with the same argument as the third call (returns the cached result).console.log(memoizedexpensivefunction(10)); // => 20// ----------------------------------------// when parameters could be array/** * @param {function} fn * @return {function} */function memoize(fn) { const cache = new map(); return function (...args) { const key = json.stringify(args); if (cache.has(key)) { return cache.get(key); } const result = fn.call(this, ...args); cache.set(key, result); return result; };}// usage examplefunction expensivemul(a, b) { console.log("computing..."); return a * b;}// create a memoized version of the function.const memoizedexpensivemul = memoize(expensivemul);// first call (computes and caches the result).console.log(memoizedexpensivemul(3, 7)); // => computing... 21// second call with the same argument (returns the cached result).console.log(memoizedexpensivemul(3, 7)); // => 21// third call with a different argument (computes and caches the new result).console.log(memoizedexpensivemul(5, 8)); // => computing... 40// fourth call with the same argument as the third call (returns the cached result).console.log(memoizedexpensivemul(5, 8)); // => 40
部分的
/** * @param {Function} fn * @param {any[]} args * @returns {Function} */function partial(fn, ...args) { return function (...restArgs) { const copyArgs = args.map((arg) => { return arg === partial.placeholder ? restArgs.shift() : arg; }); return fn.call(this, ...copyArgs, ...restArgs); };}partial.placeholder = Symbol();// Usage exampleconst func = (...args) => args;const func123 = partial(func, 1, 2, 3);console.log(func123(4)); // => [1, 2, 3, 4]
参考
伟大的前端参数对象 – mdn参数 – mdn函数组合（计算机科学）- wikipedia.org11。什么是构图？创建管道() – bfe.dev1.实现 curry() – bfe.dev2.实现带有占位符支持的 curry() – bfe.dev柯里化 – wikipedia.org14。实现通用记忆功能 – memo() – bfe.dev122。实现 memoizeone() – bfe.dev记忆 – wikipedia.org部分应用 – wikipedia.org139。实现 _.partial() – bfe.dev
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