readable.filter(fn[, options])

• fn <Function> | <AsyncFunction> 一个用于从流中过滤块的函数。
  • data <any> 从流中获取一块数据。
  • options <Object>
    • signal <AbortSignal> 如果流被销毁则中止，从而允许提前中止 fn 调用。
• options <Object>
  • concurrency <number> 是 fn 在流上同时调用的最大并发次数。默认值： 1。
  • signal <AbortSignal> 允许在信号被中止时销毁流。
• 返回：<Readable> 使用谓词 fn 过滤后的流。

此方法允许对流进行过滤。对于流中的每个数据块，将调用 fn 函数，如果它返回一个真值，该数据块将被传递到结果流中。如果 fn 函数返回一个 promise，那么该 promise 将被 await。

🌐 This method allows filtering the stream. For each chunk in the stream the fn function will be called and if it returns a truthy value, the chunk will be passed to the result stream. If the fn function returns a promise - that promise will be awaited.

import { Readable } from 'node:stream';
import { Resolver } from 'node:dns/promises';

// With a synchronous predicate.
for await (const chunk of Readable.from([1, 2, 3, 4]).filter((x) => x > 2)) {
  console.log(chunk); // 3, 4
}
// With an asynchronous predicate, making at most 2 queries at a time.
const resolver = new Resolver();
const dnsResults = Readable.from([
  'nodejs.org',
  'openjsf.org',
  'www.linuxfoundation.org',
]).filter(async (domain) => {
  const { address } = await resolver.resolve4(domain, { ttl: true });
  return address.ttl > 60;
}, { concurrency: 2 });
for await (const result of dnsResults) {
  // Logs domains with more than 60 seconds on the resolved dns record.
  console.log(result);
} 拷贝