Why is Readable.read(size) always returning the whole readable data?

[ericmorand]

I am obviously missing something obvious, but I can't figure what.

Consider the following code:

import {Readable} from "node:stream";

const readable = Readable.from('1'.repeat(1000000));
const partialData = readable.read(16);

console.log(partialData.length);

The last command always output "1000000" - that is the size of the length of the string that the Readable was created from. I expect the output size to be much lower since I explicitely ask the Readable to read only 16 bytes.

What am I missing?

How can we read partial data from a Readable?