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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Make stream internal methods support promises / async await","articleBody":"Hello all,\r\nIt would be great if streams internal methods such as `_write`, `_transform` would support also a promise based implementation.\r\n\r\nTo clarify what I mean, here's an example.\r\n\r\nClassic implementation of a writable streams that receives objects containing a `path` and a `content` and it will write a file with such content for every received chunk.\r\n\r\n## Classic implementation\r\n\r\n```javascript\r\nimport { Writable } from 'stream'\r\nimport { promises as fs } from 'fs'\r\nimport { dirname } from 'path'\r\nimport mkdirp from 'mkdirp'\r\n\r\nexport class ToFileStream extends Writable {\r\n  constructor (opts) {\r\n    super({ ...opts, objectMode: true })\r\n  }\r\n\r\n  async _write (chunk, encoding, cb) {\r\n    mkdirp(dirname(chunk.path), (err) =\u003e {\r\n      if (err) {\r\n        return cb(err)\r\n      }\r\n\r\n      fs.writeFile(chunk.path, chunk.content, cb)\r\n    })\r\n  }\r\n}\r\n```\r\n\r\nNice and standard, but as it happens with callback-based APIs, it's easy to end up with a callback hell situation and repeated code in case of conditional asynchronous work.\r\n\r\n## Desired implementation\r\n\r\n**This does not work as of today**\r\n\r\n```javascript\r\nimport { Writable } from 'stream'\r\nimport { promises as fs } from 'fs'\r\nimport { dirname } from 'path'\r\nimport mkdirp from 'mkdirp-promise'\r\n\r\nexport class ToFileStream extends Writable {\r\n  constructor (opts) {\r\n    super({ ...opts, objectMode: true })\r\n  }\r\n\r\n  async _write (chunk, encoding) {\r\n    await mkdirp(dirname(chunk.path))\r\n    return fs.writeFile(chunk.path, chunk.content)\r\n  }\r\n}\r\n```\r\n\r\nThis would feel quite clean and standard for those used to the `async` `await` style\r\n\r\n## What we can do today\r\n\r\n```javascript\r\nimport { Writable } from 'stream'\r\nimport { promises as fs } from 'fs'\r\nimport { dirname } from 'path'\r\nimport mkdirp from 'mkdirp-promise'\r\n\r\nexport class ToFileStream extends Writable {\r\n  constructor (opts) {\r\n    super({ ...opts, objectMode: true })\r\n  }\r\n\r\n  async _write (chunk, encoding, cb) {\r\n    try {\r\n      await mkdirp(dirname(chunk.path))\r\n      await fs.writeFile(chunk.path, chunk.content)\r\n      cb()\r\n    } catch (err) {\r\n      cb(err)\r\n    }\r\n  }\r\n}\r\n```\r\n\r\nIn a situation with a lot of callbacks this might help to remove the nesting, but it still feels weird to (and hard to read) to mix `async` `await` style with callbacks.\r\n\r\n---\r\n\r\nWhat do you think? Would this be something feasible without breaking existing streams implementations?","author":{"url":"https://github.com/lmammino","@type":"Person","name":"lmammino"},"datePublished":"2020-01-16T20:38:59.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":9},"url":"https://github.com/31387/node/issues/31387"}