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stream.Transform

A duplex stream that transforms input chunks into output chunks.

Since Node 0.x Spec ↗

Syntax

new Transform({ transform(chunk, enc, cb) {} })

Returns

Transform — A stream that is both readable and writable.

Examples

import { Transform } from 'node:stream';

const upper = new Transform({
  transform(chunk, _e, cb) {
    cb(null, chunk.toString().toUpperCase());
  },
});
upper.on('data', (d) => console.log(d.toString()));
upper.end('hello');
Output 
HELLO

import { Readable, Transform } from 'node:stream';
import { pipeline } from 'node:stream/promises';

const double = new Transform({
  objectMode: true,
  transform(n, _e, cb) { cb(null, n * 2); },
});
await pipeline(Readable.from([1, 2, 3]), double, async function (src) {
  for await (const v of src) console.log(v);
});
Output 
2
4
6

Notes

Call `cb(null, output)` to push transformed data, or `cb(err)` to fail. Set `objectMode: true` to pass non-Buffer values. Implement `flush(cb)` to emit trailing data after input ends.

See also