readable.find(fn[, options])

• fn <Function> | <AsyncFunction> 调用流的每个块的函数。

  ¥fn <Function> | <AsyncFunction> a function to call on each chunk of the stream.

  • data <any> 来自流的数据块。

    ¥data <any> a chunk of data from the stream.

  • options <Object>

    • signal <AbortSignal> 如果流被销毁则中止，允许提前中止 fn 调用。

      ¥signal <AbortSignal> aborted if the stream is destroyed allowing to abort the fn call early.

• options <Object>

  • concurrency <number> 一次调用流的 fn 的最大并发调用数。默认值：1。

    ¥concurrency <number> the maximum concurrent invocation of fn to call on the stream at once. Default: 1.

  • signal <AbortSignal> 如果信号中止，允许销毁流。

    ¥signal <AbortSignal> allows destroying the stream if the signal is aborted.

• 返回：<Promise> 是评估第一个块的 promise，其中 fn 使用真值进行评估，如果未找到元素，则评估 undefined。

  ¥Returns: <Promise> a promise evaluating to the first chunk for which fn evaluated with a truthy value, or undefined if no element was found.

此方法类似于 Array.prototype.find，并在流中的每个块上调用 fn 以查找具有 fn 真值的块。一旦 fn 调用的等待返回值是真实的，流就会被销毁，并且 promise 会用 fn 返回真实值的值来实现。如果对块的所有 fn 调用都返回一个假值，则 promise 通过 undefined 实现。

¥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 stat.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