Node.js by Example: Logging

Node.js provides straightforward tools for logging. The built-in console methods handle free-form output, and structured output can be done with JSON.stringify.

 
import { Writable } from "node:stream";

Node implements console.log for standard functionality similar to println in other languages. console also has .error, .info, .debug and .warn to result in different styled output.

 
console.log("standard logger")

Node specifically allows us direct access to stdout or stderr via the process object.

 
process.stdout.write("Buffer to write", err => {

The callback to execute when the data is fully written out.

 
    if (err) {
        console.log(err);
    }
});

If we desire custom output targets, we can use Writable to specify where we would like to write to.

 
let bufContents = "";
const bufStream = new Writable({
    write(chunk, _enc, cb) {
        bufContents += chunk.toString(); cb();
    },
});
bufStream.write(
    `buf:${new Date().toISOString()} hello\n`
);
process.stdout.write(
    `from buflog:${bufContents}`
);

Structured (JSON) logging

 
process.stderr.write(
    JSON.stringify({
        time: new Date().toISOString(),
        level: "INFO",
        msg: "hi there"
    }) + "\n"
);

Logging in nodejs, using module system for imports

 
$ node logging.mjs
standard logger
{
    "time":"2026-08-20T15:55:24.078Z",
    "level":"INFO",
    "msg":"hi there"
}

Next example: .

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