Console - Bun

Bun implements the standard Console API with enhanced formatting, colors, and object inspection. It’s compatible with Node.js and browsers.

Basic Logging

console.log()

Log messages to stdout:

console.log("Hello");
console.log("Number:", 42);
console.log("Object:", { name: "Alice", age: 30 });
console.log("Array:", [1, 2, 3]);

console.error()

Log errors to stderr:

console.error("Error occurred");
console.error("Error:", new Error("Something went wrong"));

console.warn()

Log warnings to stderr:

console.warn("Deprecated function");
console.warn("Warning:", "This will be removed in v2.0");

console.info()

Log informational messages:

console.info("Server started");
console.info("Port:", 3000);

console.debug()

Log debug messages:

console.debug("Debug info:", { state: "active", count: 42 });

Formatting

Format Specifiers

// %s - String
console.log("Hello %s", "World");

// %d or %i - Integer
console.log("Count: %d", 42);

// %f - Float
console.log("Pi: %f", 3.14159);

// %o - Object
console.log("Data: %o", { x: 1, y: 2 });

// %O - Object (detailed)
console.log("Details: %O", { x: 1, y: 2 });

// %c - CSS styling (in browsers)
console.log("%cStyled text", "color: blue; font-weight: bold");

Multiple Arguments

console.log("User", user, "logged in at", timestamp);

Object Inspection

Default Inspection

const obj = {
  name: "Alice",
  age: 30,
  address: {
    city: "NYC",
    zip: "10001",
  },
};

console.log(obj);
// {
//   name: "Alice",
//   age: 30,
//   address: { city: "NYC", zip: "10001" }
// }

Deep Inspection

Control inspection depth:

const nested = {
  level1: {
    level2: {
      level3: {
        level4: { value: 42 },
      },
    },
  },
};

console.log(nested);
// Default depth: 2 levels

Set depth with environment variable:

# Show 4 levels deep
bun --console-depth=4 script.ts

Or in bunfig.toml:

[console]
depth = 4

Arrays

const arr = [1, 2, 3, 4, 5];
console.log(arr);
// [1, 2, 3, 4, 5]

// Large arrays are truncated
const large = Array.from({ length: 1000 }, (_, i) => i);
console.log(large);
// [0, 1, 2, ... 997, 998, 999]

Functions

function greet(name: string) {
  return `Hello ${name}`;
}

console.log(greet);
// [Function: greet]

const arrow = (x: number) => x * 2;
console.log(arrow);
// [Function: arrow]

Classes

class User {
  constructor(public name: string) {}
  
  greet() {
    return `Hello ${this.name}`;
  }
}

const user = new User("Alice");
console.log(user);
// User { name: "Alice" }

Grouping

console.group()

Create collapsible groups:

console.group("User Details");
console.log("Name:", "Alice");
console.log("Age:", 30);
console.group("Address");
console.log("City:", "NYC");
console.log("Zip:", "10001");
console.groupEnd();
console.groupEnd();

// User Details
//   Name: Alice
//   Age: 30
//   Address
//     City: NYC
//     Zip: 10001

console.groupCollapsed()

Create collapsed groups:

console.groupCollapsed("Debug Info");
console.log("Timestamp:", Date.now());
console.log("Memory:", process.memoryUsage());
console.groupEnd();

Tables

console.table()

Display data as a table:

const users = [
  { name: "Alice", age: 30, city: "NYC" },
  { name: "Bob", age: 25, city: "LA" },
  { name: "Charlie", age: 35, city: "Chicago" },
];

console.table(users);
// ┌─────────┬─────────┬─────┬─────────┐
// │ (index)   │ name    │ age │ city    │
// ├─────────┼─────────┼─────┼─────────┤
// │ 0         │ 'Alice' │ 30  │ 'NYC'   │
// │ 1         │ 'Bob'   │ 25  │ 'LA'    │
// │ 2         │ 'Charlie' │ 35 │ 'Chicago' │
// └─────────┴─────────┴─────┴─────────┘

Select Columns

const users = [
  { name: "Alice", age: 30, city: "NYC", country: "USA" },
  { name: "Bob", age: 25, city: "LA", country: "USA" },
];

// Only show name and age columns
console.table(users, ["name", "age"]);

Objects as Tables

const obj = {
  name: "Alice",
  age: 30,
  city: "NYC",
};

console.table(obj);
// ┌───────┬────────┐
// │ (index) │ Values │
// ├───────┼────────┤
// │ name    │ 'Alice' │
// │ age     │ 30      │
// │ city    │ 'NYC'   │
// └───────┴────────┘

Timing

console.time()

Measure execution time:

console.time("operation");

// Do some work
for (let i = 0; i < 1000000; i++) {
  Math.sqrt(i);
}

console.timeEnd("operation");
// operation: 15.234ms

console.timeLog()

Log intermediate times:

console.time("task");

// Step 1
processStep1();
console.timeLog("task", "Step 1 complete");
// task: 10ms Step 1 complete

// Step 2
processStep2();
console.timeLog("task", "Step 2 complete");
// task: 25ms Step 2 complete

console.timeEnd("task");
// task: 30ms

Multiple Timers

console.time("total");
console.time("fetch");
await fetchData();
console.timeEnd("fetch");

console.time("process");
await processData();
console.timeEnd("process");

console.timeEnd("total");

Counting

console.count()

Count function calls:

function processItem(item: string) {
  console.count("processItem");
  // Process item
}

processItem("a");
// processItem: 1
processItem("b");
// processItem: 2
processItem("c");
// processItem: 3

console.countReset()

Reset counter:

console.count("requests");
console.count("requests");
// requests: 2

console.countReset("requests");
console.count("requests");
// requests: 1

Labeled Counters

function handleRequest(type: string) {
  console.count(type);
}

handleRequest("GET");  // GET: 1
handleRequest("POST"); // POST: 1
handleRequest("GET");  // GET: 2

Assertions

console.assert()

Log error if assertion fails:

const value = 5;
console.assert(value > 0, "Value must be positive");
// No output (assertion passed)

console.assert(value > 10, "Value must be greater than 10");
// Assertion failed: Value must be greater than 10

With Objects

const user = { name: "Alice", age: 30 };
console.assert(user.age >= 18, "User must be adult", { user });

Stack Traces

console.trace()

Print stack trace:

function outer() {
  function inner() {
    console.trace("Trace:");
  }
  inner();
}

outer();
// Trace:
//   at inner (file.ts:3:13)
//   at outer (file.ts:5:3)
//   at <anonymous> (file.ts:8:1)

Clearing

console.clear()

Clear console (terminal only):

console.log("Message 1");
console.log("Message 2");
console.clear(); // Clears terminal
console.log("Message 3");

Colors

Bun automatically colors output in terminals:

// Errors in red
console.error("Error message");

// Warnings in yellow
console.warn("Warning message");

// Objects with syntax highlighting
console.log({ key: "value", num: 42 });

Disable colors:

NO_COLOR=1 bun script.ts

Or:

bun script.ts --no-color

Custom Inspection

inspect Symbol

class User {
  constructor(public name: string, private password: string) {}
  
  [Symbol.for("nodejs.util.inspect.custom")]() {
    return `User { name: ${this.name} }`;
  }
}

const user = new User("Alice", "secret123");
console.log(user);
// User { name: Alice }

toJSON()

class Point {
  constructor(public x: number, public y: number) {}
  
  toJSON() {
    return { x: this.x, y: this.y };
  }
}

const p = new Point(10, 20);
console.log(p);
// Point { x: 10, y: 20 }

Best Practices

Use appropriate log levels

console.debug("Verbose debug info");
console.log("Normal output");
console.warn("Warning message");
console.error("Error occurred");

Group related logs

console.group("API Request");
console.log("URL:", url);
console.log("Method:", method);
console.log("Headers:", headers);
console.groupEnd();

Use timers for performance

console.time("database-query");
await db.query(sql);
console.timeEnd("database-query");

Table for structured data
```
console.table(results);
```

Assertions for debugging

console.assert(user.id, "User ID is required");

Production Logging

For production apps, consider using a logging library:

import { createLogger } from "some-logger";

const logger = createLogger({
  level: process.env.LOG_LEVEL || "info",
  format: "json",
});

logger.info("Server started", { port: 3000 });
logger.error("Request failed", { error, url });

Platform Differences

Bun vs Node.js

Colors: Bun has better default colors
Performance: Bun’s console is faster
Depth: Bun defaults to depth 2, Node to unlimited

Bun vs Browsers

Streams: Bun writes to stdout/stderr, browsers to DevTools
Styling: CSS styling (%c) only works in browsers
Persistence: Browser console persists between reloads

API Reference

Logging Methods

console.log(...args: any[]): void
console.error(...args: any[]): void
console.warn(...args: any[]): void
console.info(...args: any[]): void
console.debug(...args: any[]): void

Grouping

console.group(label?: string): void
console.groupCollapsed(label?: string): void
console.groupEnd(): void

Tables

console.table(data: any, columns?: string[]): void

Timing

console.time(label?: string): void
console.timeLog(label?: string, ...args: any[]): void
console.timeEnd(label?: string): void

Counting

console.count(label?: string): void
console.countReset(label?: string): void

Other

console.assert(condition: boolean, ...args: any[]): void
console.trace(...args: any[]): void
console.clear(): void

Core Runtime

APIs

HTTP & WebSocket

Data & Storage

System & Process

Utilities

​Basic Logging

​console.log()

​console.error()

​console.warn()

​console.info()

​console.debug()

​Formatting

​Format Specifiers

​Multiple Arguments

​Object Inspection

​Default Inspection

​Deep Inspection

​Arrays

​Functions

​Classes

​Grouping

​console.group()

​console.groupCollapsed()

​Tables

​console.table()

​Select Columns

​Objects as Tables

​Timing

​console.time()

​console.timeLog()

​Multiple Timers

​Counting

​console.count()

​console.countReset()

​Labeled Counters

​Assertions

​console.assert()

​With Objects

​Stack Traces

​console.trace()

​Clearing

​console.clear()

​Colors

​Custom Inspection

​inspect Symbol

​toJSON()

​Best Practices

​Production Logging

​Platform Differences

​Bun vs Node.js

​Bun vs Browsers

​API Reference

​Logging Methods

​Grouping

​Tables

​Timing

​Counting

​Other

Build docs developers (and LLMs) love

Basic Logging

console.log()

console.error()

console.warn()

console.info()

console.debug()

Formatting

Format Specifiers

Multiple Arguments

Object Inspection

Default Inspection

Deep Inspection

Arrays

Functions

Classes

Grouping

console.group()

console.groupCollapsed()

Tables

console.table()

Select Columns

Objects as Tables

Timing

console.time()

console.timeLog()

Multiple Timers

Counting

console.count()

console.countReset()

Labeled Counters

Assertions

console.assert()

With Objects

Stack Traces

console.trace()

Clearing

console.clear()

Colors

Custom Inspection

inspect Symbol

toJSON()

Best Practices

Production Logging

Platform Differences

Bun vs Node.js

Bun vs Browsers

API Reference

Logging Methods

Grouping

Tables

Timing

Counting

Other