readable.find(fn[, options])

• fn <Function> | <AsyncFunction> 对流的每个数据块调用的函数。
  • data <any> 来自流的一段数据。
  • options <Object>
    • signal <AbortSignal> 如果流被销毁，则会中止，从而允许提前终止 fn 调用。
• options <Object>
  • concurrency <number> fn 在流上一次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：<Promise> 一个 promise，其值为第一个 fn 计算结果为真值的块，如果没有找到这样的元素，则为 undefined。

此方法类似于 Array.prototype.find，会在流中的每个块上调用 fn，以查找 fn 返回真值的块。一旦某次 fn 调用的 await 返回值为真，流将被销毁，并且该 promise 会以 fn 返回真值的那个值被解决。如果所有块上的 fn 调用都返回假值，则该 promise 会以 undefined 被解决。

🌐 This method is similar to Array.prototype.find and calls fn on each chunk in the stream to find a chunk with a truthy value for fn. Once an fn call's awaited return value is truthy, the stream is destroyed and the promise is fulfilled with value for which fn returned a truthy value. If all of the fn calls on the chunks return a falsy value, the promise is fulfilled with undefined.

import { Readable } from 'node:stream';
import { stat } from 'node:fs/promises';

// With a synchronous predicate.
await Readable.from([1, 2, 3, 4]).find((x) => x > 2); // 3
await Readable.from([1, 2, 3, 4]).find((x) => x > 0); // 1
await Readable.from([1, 2, 3, 4]).find((x) => x > 10); // undefined

// With an asynchronous predicate, making at most 2 file checks at a time.
const foundBigFile = await Readable.from([
  'file1',
  'file2',
  'file3',
]).find(async (fileName) => {
  const stats = await stat(fileName);
  return stats.size > 1024 * 1024;
}, { concurrency: 2 });
console.log(foundBigFile); // File name of large file, if any file in the list is bigger than 1MB
console.log('done'); // Stream has finished 拷贝