memoize 记忆函数

/** @template T @typedef {function(): T} FunctionReturning */

/**
 * @template T
 * @param {FunctionReturning<T>} fn memorized function
 * @returns {FunctionReturning<T>} new function
 */
const memoize = fn => {
  let cache = false;
  /** @type {T} */
  let result = undefined;
  return () => {
    if (cache) {
      return result;
    } else {
      result = fn();
      cache = true;
      // Allow to clean up memory for fn
      // and all dependent resources
      fn = undefined;
      return result;
    }
  };
};

测试：

let newFn = memoize(() => {
  console.log('执行')
  return 'hello'
})

console.log(newFn())
console.log(newFn())

然后升级一下，支持调用内部函数：

/**
 * @template {Function} T
 * @param {function(): T} factory factory function
 * @returns {T} function
 */
const lazyFunction = factory => {
  const fac = memoize(factory);
  const f = /** @type {any} */ (
    (...args) => {
      return fac()(...args);
    }
  );
  return /** @type {T} */ (f);
};

测试代码：

let newFn = lazyFunction(() => {
  console.log('执行')
  return (val) => {
    console.log(val)
    return val
  }
})
console.log(newFn(1))
console.log(newFn(1))