Prettifier Factory

/**
 * Creates a prettifier function for transforming log data
 * @param options - Configuration for the prettifier
 * @returns Function that accepts log data and returns prettified strings
 */
function prettyFactory(options: PrettyOptions): LogPrettifierFunc;

/**
 * The prettifier function returned by prettyFactory
 * @param inputData - A log string (JSON) or log object
 * @returns Prettified log string with line ending
 */
type LogPrettifierFunc = (inputData: string | object) => string;

const { prettyFactory } = require('pino-pretty');

// Create a prettifier with custom options
const prettifier = prettyFactory({
  colorize: true,
  translateTime: 'HH:MM:ss',
  ignore: 'pid,hostname'
});

// Use with JSON string input
const logLine = '{"level":30,"time":1522431328992,"msg":"hello world","pid":42,"hostname":"foo"}';
const pretty = prettifier(logLine);
console.log(pretty);
// Output: [10:30:45] INFO: hello world

// Use with object input
const logObject = {
  level: 30,
  time: Date.now(),
  msg: 'user logged in',
  userId: 123
};
const prettyObj = prettifier(logObject);
console.log(prettyObj);
// Output: [10:32:15] INFO: user logged in
//     userId: 123

// Example: Custom log processing pipeline
const { prettyFactory } = require('pino-pretty');

const prettifier = prettyFactory(options);

function processLogLine(line) {
  const prettyLine = prettifier(line);
  // Send to custom destination
  return prettyLine;
}

const { prettyFactory } = require('pino-pretty');
const fs = require('fs');

// Create prettifier
const prettifier = prettyFactory({
  colorize: false,
  translateTime: 'SYS:standard',
  singleLine: true
});

// Process log file line by line
const readline = require('readline');
const rl = readline.createInterface({
  input: fs.createReadStream('./logs/app.ndjson'),
  crlfDelay: Infinity
});

rl.on('line', (line) => {
  const pretty = prettifier(line);
  console.log(pretty);
});

/**
 * Behavior for non-JSON input:
 * - If input cannot be parsed as JSON, returns input + EOL unchanged
 * - If parsed JSON is not an object, returns input + EOL unchanged
 */

const { prettyFactory } = require('pino-pretty');

const prettifier = prettyFactory({ colorize: true });

// Valid JSON log
const validLog = prettifier('{"level":30,"msg":"hello"}');
// Returns prettified output

// Invalid JSON
const invalidJson = prettifier('this is not json');
// Returns: "this is not json\n"

// Valid JSON but not a log object
const notObject = prettifier('"just a string"');
// Returns: "\"just a string\"\n"

/**
 * When minimumLevel is set, logs below that level return undefined
 * This allows filtering in the prettifier itself
 */

const { prettyFactory } = require('pino-pretty');

const prettifier = prettyFactory({
  minimumLevel: 'info',  // Filter out trace and debug
  colorize: true
});

// This returns prettified output
const infoLog = prettifier({ level: 30, msg: 'info message' });
console.log(infoLog); // [10:30:45] INFO: info message

// This returns undefined (filtered out)
const debugLog = prettifier({ level: 20, msg: 'debug message' });
console.log(debugLog); // undefined

// Handle filtering in your code
function processLog(logData) {
  const result = prettifier(logData);
  if (result !== undefined) {
    console.log(result);
  }
}

/**
 * Prettifier functions are stateless:
 * - Configuration is bound at creation time
 * - Same prettifier can be called concurrently
 * - Safe to use across multiple threads/workers
 */

const { prettyFactory } = require('pino-pretty');

// Create once, use many times
const prettifier = prettyFactory({ colorize: true });

// Can be called concurrently
const logs = [
  '{"level":30,"msg":"log 1"}',
  '{"level":40,"msg":"log 2"}',
  '{"level":30,"msg":"log 3"}'
];

// Process in parallel (example with worker threads)
const results = logs.map(log => prettifier(log));

// Safe to share across workers
const { Worker } = require('worker_threads');
// Pass prettifier configuration to workers, not the function itself
const config = { colorize: true, translateTime: 'HH:MM:ss' };
// Workers create their own prettifier with same config

// All PrettyOptions are supported:
// - Display options (colorize, singleLine, hideObject, etc.)
// - Key mapping (messageKey, levelKey, timestampKey, etc.)
// - Formatting (translateTime, messageFormat, errorProps, etc.)
// - Filtering (minimumLevel, ignore, include)
// - Custom prettifiers and colors

const { prettyFactory } = require('pino-pretty');

// Complex configuration
const prettifier = prettyFactory({
  // Display
  colorize: true,
  levelFirst: true,
  singleLine: false,

  // Custom keys
  messageKey: 'message',
  levelKey: 'severity',
  timestampKey: 'timestamp',

  // Formatting
  translateTime: 'SYS:yyyy-mm-dd HH:MM:ss',
  messageFormat: '{levelLabel} [{pid}] {msg}',

  // Filtering
  ignore: 'hostname,pid',
  minimumLevel: 'info',

  // Custom prettifiers
  customPrettifiers: {
    time: (timestamp) => new Date(timestamp).toISOString(),
    userId: (id) => `USER:${id}`
  }
});

const log = {
  severity: 30,
  timestamp: Date.now(),
  message: 'User action',
  userId: 12345,
  hostname: 'server1',
  pid: 5678
};

console.log(prettifier(log));
// Output: INFO [5678] User action
//     userId: USER:12345