Classic utilities

1function cloneJsonStyle(value) {2  if (value === null || typeof value !== "object") return value;3  if (Array.isArray(value)) return value.map(cloneJsonStyle);4  const copy = {};5  for (const key of Object.keys(value)) {6    copy[key] = cloneJsonStyle(value[key]);7  }8  return copy;9}10 11const profile = { name: "Ada" };12profile.self = profile;13console.log(cloneJsonStyle(profile));

1function deepEqual(a, b, seen = new WeakMap()) {2  if (Object.is(a, b)) return true;3  if (a === null || b === null || typeof a !== "object" || typeof b !== "object") return false;4  const known = seen.get(a);5  if (known?.has(b)) return true;6  if (!known) seen.set(a, new WeakSet([b]));7  else known.add(b);8  if (Object.getPrototypeOf(a) !== Object.getPrototypeOf(b)) return false;9  if (a instanceof Date || b instanceof Date) return a instanceof Date && b instanceof Date && Object.is(a.getTime(), b.getTime());10  if (a instanceof RegExp || b instanceof RegExp) return a instanceof RegExp && b instanceof RegExp && a.source === b.source && a.flags === b.flags && a.lastIndex === b.lastIndex;11  if (Array.isArray(a) || Array.isArray(b)) {12    return Array.isArray(a) && Array.isArray(b) && a.length === b.length && a.every((item, index) => deepEqual(item, b[index], seen));13  }14  if (a instanceof Map || b instanceof Map) {15    if (!(a instanceof Map) || !(b instanceof Map) || a.size !== b.size) return false;16    const unmatched = [...b.entries()];17    return [...a.entries()].every(([key, value]) => {18      const index = unmatched.findIndex(([otherKey, otherValue]) => deepEqual(key, otherKey, seen) && deepEqual(value, otherValue, seen));19      if (index === -1) return false;20      unmatched.splice(index, 1);21      return true;22    });23  }24  if (a instanceof Set || b instanceof Set) {25    if (!(a instanceof Set) || !(b instanceof Set) || a.size !== b.size) return false;26    const unmatched = [...b.values()];27    return [...a.values()].every((value) => {28      const index = unmatched.findIndex((other) => deepEqual(value, other, seen));29      if (index === -1) return false;30      unmatched.splice(index, 1);31      return true;32    });33  }34  const aKeys = Reflect.ownKeys(a);35  const bKeys = Reflect.ownKeys(b);36  if (aKeys.length !== bKeys.length) return false;37  const bKeySet = new Set(bKeys);38  return aKeys.every((key) => bKeySet.has(key) && deepEqual(a[key], b[key], seen));39}40 41const left = { n: NaN, z: -0, list: [1, { x: 2 }] };42const right = { list: [1, { x: 2 }], z: 0, n: NaN };43console.log(deepEqual(left, right));44right.z = -0;45console.log(deepEqual(left, right));46left.self = left;47right.self = right;48console.log(deepEqual(left, right));49console.log(deepEqual(new Map([[{ id: 1 }, new Set([2])]]), new Map([[{ id: 1 }, new Set([2])]])));

1const __ = Symbol("placeholder");2function curry(fn, arity = fn.length) {3  return function curried(...args) {4    const complete = args.length >= arity && args.slice(0, arity).every((arg) => arg !== __);5    if (complete) return fn.apply(this, args.slice(0, arity));6    return function collect(...more) {7      const merged = args.map((arg) => arg === __ && more.length ? more.shift() : arg).concat(more);8      return curried.apply(this, merged);9    };10  };11}12 13const format = (greeting, name, punctuation) => greeting + ", " + name + punctuation;14const greet = curry(format);15console.log(greet("Hi")("Ada")("!"));16console.log(greet("Hi", "Lin")("."));17console.log(greet(__, "Grace")("Hello")("!"));

1const compose = (...fns) => (input) =>2  fns.reduceRight((value, fn) => fn(value), input);3const pipe = (...fns) => (input) =>4  fns.reduce((value, fn) => fn(value), input);5const pipeAsync = (...fns) => (input) =>6  fns.reduce((promise, fn) => promise.then(fn), Promise.resolve(input));7 8const trim = (text) => text.trim();9const lower = (text) => text.toLowerCase();10const dash = (text) => text.replaceAll(" ", "-");11 12console.log(compose(dash, lower, trim)("  Utility Lesson  "));13console.log(pipe(trim, lower, dash)("  Utility Lesson  "));14pipeAsync(15  async (id) => ({ id, role: "admin" }),16  async (user) => user.role.toUpperCase(),17)(7).then(console.log);

1function memoize(fn, resolver = (...args) => JSON.stringify(args)) {2  const cache = new Map();3  function memoized(...args) {4    const key = resolver(...args);5    if (cache.has(key)) return cache.get(key);6    const result = fn.apply(this, args);7    cache.set(key, result);8    return result;9  }10  memoized.cache = cache;11  memoized.clear = () => cache.clear();12  return memoized;13}14 15function once(fn) {16  let called = false;17  let result;18  let error;19  let threw = false;20  return function runOnce(...args) {21    if (!called) {22      called = true;23      try { result = fn.apply(this, args); }24      catch (caught) { threw = true; error = caught; throw caught; }25    }26    if (threw) throw error;27    return result;28  };29}30 31let calls = 0;32const area = memoize((w, h) => { calls++; return w * h; }, (w, h) => w + "x" + h);33console.log(area(3, 4));34console.log(area(3, 4));35console.log(calls);36area.clear();37console.log(area(3, 4));38console.log(calls);39 40const button = { label: "save", init: once(function (suffix) { return this.label + suffix; }) };41console.log(button.init("!"));42console.log(button.init("?"));

1function createFakeClock() {2  let now = 0;3  let nextId = 1;4  const tasks = [];5  return {6    now: () => now,7    setTimeout(callback, wait) {8      const task = { id: nextId++, time: now + wait, callback, cleared: false };9      tasks.push(task);10      return task.id;11    },12    clearTimeout(id) {13      for (const task of tasks) if (task.id === id) task.cleared = true;14    },15    tick(ms) {16      const end = now + ms;17      while (true) {18        const ready = tasks.filter((task) => !task.cleared && task.time <= end).sort((a, b) => a.time - b.time)[0];19        if (!ready) break;20        ready.cleared = true;21        now = ready.time;22        ready.callback();23      }24      now = end;25    },26  };27}28 29function debounce(fn, wait, clock = { setTimeout, clearTimeout }) {30  let timeout;31  return function debounced(...args) {32    clock.clearTimeout(timeout);33    timeout = clock.setTimeout(() => fn.apply(this, args), wait);34  };35}36 37function throttle(fn, wait, clock = { now: Date.now, setTimeout, clearTimeout }) {38  let lastRun = -Infinity;39  let timeout;40  let lastArgs;41  let lastThis;42  return function throttled(...args) {43    const remaining = wait - (clock.now() - lastRun);44    lastArgs = args;45    lastThis = this;46    if (remaining <= 0) {47      if (timeout !== undefined) clock.clearTimeout(timeout);48      timeout = undefined;49      lastRun = clock.now();50      fn.apply(lastThis, lastArgs);51    } else if (timeout === undefined) {52      timeout = clock.setTimeout(() => {53        timeout = undefined;54        lastRun = clock.now();55        fn.apply(lastThis, lastArgs);56      }, remaining);57    }58  };59}60 61const log = [];62const clock = createFakeClock();63const save = debounce((value) => log.push("debounced " + value), 100, clock);64save("a");65clock.tick(50);66save("b");67clock.tick(100);68const paint = throttle((value) => log.push("throttled " + value), 100, clock);69paint("one");70clock.tick(20);71paint("two");72clock.tick(100);73console.log(log.join(" | "));

1function get(obj, path, defaultValue) {2  const parts = path.replace(/\[(\w+)\]/g, ".$1").split(".").filter(Boolean);3  let cursor = obj;4  for (const part of parts) {5    if (cursor == null) return defaultValue;6    cursor = cursor[part];7  }8  return cursor === undefined ? defaultValue : cursor;9}10 11const data = { users: [{ profile: { name: "Ada" } }] };12console.log(get(data, "users[0].profile.name", "Unknown"));13console.log(get(data, "users[1].profile.name", "Unknown"));