JavaScript惰性求值_延迟计算与无限序列实现

const lazyAdd = (a, b) => () => a + b;
const computation = lazyAdd(2, 3);
// 此时并未计算
console.log(computation()); // 直到调用才输出 5

function* naturalNumbers() {
  let n = 1;
  while (true) {
    yield n++;
  }
}
<p>const numbers = naturalNumbers();
console.log(numbers.next().value); // 1
console.log(numbers.next().value); // 2
console.log(numbers.next().value); // 3</p>

function* map(iterable, fn) {
  for (const item of iterable) {
    yield fn(item);
  }
}
<p>function* filter(iterable, predicate) {
for (const item of iterable) {
if (predicate(item)) yield item;
}
}</p><p>// 使用：生成前10个偶数的平方
const result = [...take(
map(
filter(naturalNumbers(), n => n % 2 === 0),
n => n ** 2
),
10
)];</p>

function* take(iterable, count) {
  let taken = 0;
  for (const item of iterable) {
    if (taken >= count) return;
    yield item;
    taken++;
  }
}

function* fibonacci() {
  let a = 0, b = 1;
  while (true) {
    yield a;
    [a, b] = [b, a + b];
  }
}