Logging

console.log((new Date()).toISOString(), 'hello world')
 
// structured (JSON) output — Node.js has no bundled structured logger, so
// logging a plain object as JSON is the common baseline
console.log(JSON.stringify({ level: 'info', msg: 'hello world', time: new Date().toISOString() }))

package main
 
import (
	"log"
	"log/slog"
)
 
func main() {
	// Package `log` writes to standard error and prints the date and time of each logged message
	log.Println("hello world")
 
	// log/slog adds structured, leveled logging to the standard library
	slog.Info("hello world", "count", 1)
}

// Cargo.toml: tracing = "0.1", tracing-subscriber = { version = "0.3", features = ["json"] }
use tracing::info;
use tracing_subscriber::fmt;
 
fn main() {
    // default format: adds a timestamp + level automatically
    let plain = fmt().with_ansi(false).finish();
    tracing::subscriber::with_default(plain, || {
        info!("hello world");
    });
 
    // structured (JSON), leveled logging
    let json = fmt().json().finish();
    tracing::subscriber::with_default(json, || {
        info!(count = 1, "hello world");
    });
}

import Foundation
 
struct LogEntry: Encodable {
    let level: String
    let msg: String
    let time: String
}
 
let timestamp = ISO8601DateFormatter().string(from: Date())
print(timestamp, "hello world")
 
// structured (JSON) output — Swift has no bundled structured logger like Go's slog, so
// encoding a Codable struct as JSON is the common baseline (like Node.js's JSON.stringify)
let encoder = JSONEncoder()
encoder.outputFormatting = .sortedKeys // default key order isn't guaranteed; force alphabetical for stability
let entry = LogEntry(level: "info", msg: "hello world", time: timestamp)
let data = try! encoder.encode(entry)
print(String(data: data, encoding: .utf8)!)

void main() {
    // System.Logger is java.base's logging API; it adds a timestamp via the default console backend
    System.Logger logger = System.getLogger("example");
    logger.log(System.Logger.Level.INFO, "hello world");
 
    // structured (JSON) output — java.base has no built-in JSON builder, so hand-building the
    // string is the common baseline (just like Node.js), or reach for a library like Jackson
    String time = Instant.now().toString();
    String json = "{\"level\":\"info\",\"msg\":\"hello world\",\"time\":\"%s\"}".formatted(time);
    IO.println(json);
}