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js实现poll函数

2026-03-15 19:20:33JavaScript

实现 Poll 函数的方法

在 JavaScript 中，poll 函数通常用于定期检查某个条件是否满足，直到条件为真或超时。以下是几种实现方式：

基础实现

使用 setInterval 定期检查条件，满足后清除定时器：

function poll(fn, condition, interval = 100, timeout = 5000) {
  const endTime = Date.now() + timeout;
  const checkCondition = () => {
    const result = fn();
    if (condition(result)) {
      return Promise.resolve(result);
    }
    if (Date.now() > endTime) {
      return Promise.reject(new Error('Timeout exceeded'));
    }
    return new Promise(resolve => {
      setTimeout(() => resolve(checkCondition()), interval);
    });
  };
  return checkCondition();
}

使用 async/await

更现代的异步实现方式：

async function poll(fn, condition, interval = 100, timeout = 5000) {
  const endTime = Date.now() + timeout;
  while (true) {
    const result = await fn();
    if (condition(result)) return result;
    if (Date.now() > endTime) throw new Error('Timeout exceeded');
    await new Promise(resolve => setTimeout(resolve, interval));
  }
}

带取消功能的实现

添加取消机制，允许提前终止轮询：

js实现poll函数

function cancellablePoll(fn, condition, interval = 100, timeout = 5000) {
  let timer;
  let rejected = false;
  const promise = new Promise((resolve, reject) => {
    const endTime = Date.now() + timeout;
    const checkCondition = () => {
      if (rejected) return;
      const result = fn();
      if (condition(result)) {
        resolve(result);
      } else if (Date.now() > endTime) {
        reject(new Error('Timeout exceeded'));
      } else {
        timer = setTimeout(checkCondition, interval);
      }
    };
    checkCondition();
  });
  promise.cancel = () => {
    clearTimeout(timer);
    rejected = true;
  };
  return promise;
}

使用示例

// 检查某个元素是否出现在DOM中
poll(
  () => document.querySelector('.target-element'),
  element => element !== null,
  200,
  10000
).then(element => {
  console.log('Element found:', element);
}).catch(err => {
  console.error('Polling failed:', err);
});

// 可取消的示例
const polling = cancellablePoll(
  () => Math.random(),
  val => val > 0.9,
  100,
  5000
);

// 可以调用 polling.cancel() 提前终止
setTimeout(() => polling.cancel(), 2000);

polling.then(val => {
  console.log('Got value:', val);
}).catch(err => {
  console.error('Polling failed:', err);
});