tessl/npm-logform

An mutable object-based log format designed for chaining & objectMode streams.

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Text Formatting

Name: tessl/npm-logform
Author: tessl

Basic text formatting operations for messages and levels, providing simple text transformations and custom templating.

Capabilities

Align Format

Adds a tab delimiter before the message to align it in the same place.

/**
 * Creates an align format that adds tab indentation
 * @returns {Format} Align format instance
 */
function align();

Usage Examples:

const { format } = require('logform');

const alignFormat = format.align();
const result = alignFormat.transform({
  level: 'info',
  message: 'my message'
});
// Result: { level: 'info', message: '\tmy message' }

Simple Format

Creates a simple text representation of log entries in the format level: message with optional metadata.

/**
 * Creates a simple text format
 * @returns {Format} Simple format instance
 */
function simple();

The simple format produces output in this structure:

${level}: ${message} if no additional metadata
${level}: ${message} ${JSON.stringify(metadata)} if additional properties exist

Usage Examples:

const { format } = require('logform');
const { MESSAGE } = require('triple-beam');

const simpleFormat = format.simple();

// Basic usage
const result1 = simpleFormat.transform({
  level: 'info',
  message: 'Hello world'
});
console.log(result1[MESSAGE]); // "info: Hello world"

// With metadata
const result2 = simpleFormat.transform({
  level: 'error',
  message: 'Something failed',
  errorCode: 500,
  timestamp: '2023-01-01T00:00:00Z'
});
console.log(result2[MESSAGE]); 
// "error: Something failed {\"errorCode\":500,\"timestamp\":\"2023-01-01T00:00:00Z\"}"

Printf Format

Creates a custom logging format using a template function.

/**
 * Creates a printf-style format with custom template function
 * @param {Function} templateFn - Function that receives info object and returns formatted string
 * @returns {Format} Printf format instance
 */
function printf(templateFn);

Usage Examples:

const { format } = require('logform');

// Basic template
const myFormat = format.printf((info) => {
  return `${info.level}: ${info.message}`;
});

const result = myFormat.transform({
  level: 'info',
  message: 'Hello world'
});

// With timestamp and metadata
const detailedFormat = format.printf((info) => {
  const { level, message, timestamp, ...meta } = info;
  const metaStr = Object.keys(meta).length ? JSON.stringify(meta, null, 2) : '';
  return `[${timestamp}] ${level}: ${message} ${metaStr}`;
});

// Combined with other formats
const combinedFormat = format.combine(
  format.timestamp(),
  format.printf((info) => {
    return `${info.timestamp} [${info.level}]: ${info.message}`;
  })
);

Printf Class

The internal class used by the printf format.

/**
 * Internal Printf class that handles template formatting
 */
class Printf {
  /**
   * @param {Function} templateFn - Template function for formatting
   */
  constructor(templateFn);
  
  /** Template function that formats info objects */
  template: Function;
  
  /**
   * Transform method that applies the template
   * @param {Object} info - Log info object
   * @returns {Object} Info object with MESSAGE symbol set
   */
  transform(info);
}