std:log

Contents

• Log

Log

import { Log } from "std:log";

Run

Leveled logging to stderr. The functions can also be imported one by one, e.g. import { info, warn } from "std:log".

Log Levels

Level	Value	Description
TRACE	0	Very detailed debugging
DEBUG	1	Debug information
INFO	2	General information (default)
WARN	3	Warnings
ERROR	4	Errors
FATAL	5	Fatal errors
OFF	6	Disable all logging

The level belongs to the script. It does not depend on RUST_LOG.

Methods

Each logging method takes any number of values and joins them with spaces.

fn trace(...args)

Log a trace-level message.

import { Log } from "std:log";

Log.setLevel("trace");
Log.trace("Entering function", "parseConfig");

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fn debug(...args)

Log a debug-level message.

import { Log } from "std:log";

let x = 42;
Log.setLevel("debug");
Log.debug("Variable value:", x);

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fn info(...args)

Log an info-level message.

import { Log } from "std:log";

Log.info("Server started on port", 8080);

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fn warn(...args)

Log a warning-level message.

import { Log } from "std:log";

Log.warn("Deprecated API used");

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fn error(...args)

Log an error-level message.

import { Log } from "std:log";

Log.error("Failed to connect:", "connection refused");

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fn fatal(...args)

Log a fatal-level message. It only logs; it does not stop the program.

import { Log } from "std:log";

Log.fatal("Unrecoverable error, shutting down");

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fn setLevel(level: String | Int)

Set the minimum log level. Messages below this level are dropped. Takes a level name ("trace" to "fatal", or "off") or a number from 0 to 6.

import { Log } from "std:log";

Log.setLevel("debug");  // Show debug and above
Log.setLevel(4);        // Show error and above only
Log.setLevel("off");    // Disable all logging

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fn getLevel(): String

Get the current log level as a lowercase string.

import { Log } from "std:log";

print(Log.getLevel());  // info

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fn create(prefix: String): Map

Create a logger that starts each message with prefix. It has the methods trace, debug, info, warn, error, and fatal, and uses the global level.

import { Log } from "std:log";

let dbLog = Log.create("[DB]");
dbLog.info("Connected to database");  // ... INFO  - [DB] Connected to database

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Example

import { Log } from "std:log";

// Set level to debug for development
Log.setLevel("debug");

// Log different types of data
Log.info("Application started");
Log.debug("Config:", { port: 8080, debug: true });
Log.warn("Cache miss for key:", "user:123");
Log.error("Request failed:", { status: 500, message: "Internal error" });

// Create module-specific loggers
let authLog = Log.create("[Auth]");
authLog.info("User logged in:", "john@example.com");

// In production, set to warn or error
Log.setLevel("warn");

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Output Format

Each line has the local time, the level, and the message:

[2026-02-01T01:49:11] INFO  - Application started
[2026-02-01T01:49:11] DEBUG - Config: {port: 8080, debug: true}
[2026-02-01T01:49:11] WARN  - Cache miss for key: user:123
[2026-02-01T01:49:11] ERROR - Request failed: {status: 500, message: Internal error}
[2026-02-01T01:49:11] INFO  - [Auth] User logged in: john@example.com