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GeezerVison is showing github.com — doc: update `stream.reduce` concurrency note by rluvaton · Pull Request #47166 · nodejs/node
doc: update
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@@ -2501,21 +2501,44 @@ This method calls `fn` on each chunk of the stream in order, passing it the | |
| result from the calculation on the previous element. It returns a promise for | ||
| the final value of the reduction. | ||
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| The reducer function iterates the stream element-by-element which means that | ||
| there is no `concurrency` parameter or parallelism. To perform a `reduce` | ||
| concurrently, it can be chained to the [`readable.map`][] method. | ||
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| If no `initial` value is supplied the first chunk of the stream is used as the | ||
| initial value. If the stream is empty, the promise is rejected with a | ||
| `TypeError` with the `ERR_INVALID_ARGS` code property. | ||
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| ```mjs | ||
| import { Readable } from 'node:stream'; | ||
| import { readdir, stat } from 'node:fs/promises'; | ||
| import { join } from 'node:path'; | ||
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| const ten = await Readable.from([1, 2, 3, 4]).reduce((previous, data) => { | ||
| return previous + data; | ||
| }); | ||
| console.log(ten); // 10 | ||
| const directoryPath = './src'; | ||
| const filesInDir = await readdir(directoryPath); | ||
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| const folderSize = await Readable.from(filesInDir) | ||
| .reduce(async (totalSize, file) => { | ||
| const { size } = await stat(join(directoryPath, file)); | ||
| return totalSize + size; | ||
| }, 0); | ||
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| console.log(folderSize); | ||
| ``` | ||
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There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. Updated this example as well so the refactor can be more obvious
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| The reducer function iterates the stream element-by-element which means that | ||
| there is no `concurrency` parameter or parallelism. To perform a `reduce` | ||
| concurrently, you can extract the async function to [`readable.map`][] method. | ||
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| ```mjs | ||
| import { Readable } from 'node:stream'; | ||
| import { readdir, stat } from 'node:fs/promises'; | ||
| import { join } from 'node:path'; | ||
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| const directoryPath = './src'; | ||
| const filesInDir = await readdir(directoryPath); | ||
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| const folderSize = await Readable.from(filesInDir) | ||
| .map((file) => stat(join(directoryPath, file)), { concurrency: 2 }) | ||
| .reduce((totalSize, { size }) => totalSize + size, 0); | ||
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| console.log(folderSize); | ||
| ``` | ||
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| ### Duplex and transform streams | ||
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