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 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