loglevel-plugin-prefix/lib/loglevel-plugin-prefix.js

(function (root, factory) {
  if (typeof define === 'function' && define.amd) {
    define(factory);
  } else if (typeof module === 'object' && module.exports) {
    module.exports = factory();
  } else {
    root.prefix = factory(root);
  }
}(this, function (root) {
  'use strict';

  var merge = function merge(target) {
    var i = 1;
    var length = arguments.length;
    var key;
    for (; i < length; i++) {
      for (key in arguments[i]) {
        if (Object.prototype.hasOwnProperty.call(arguments[i], key)) {
          target[key] = arguments[i][key];
        }
      }
    }
    return target;
  };

  var defaults = {
    template: '[%t] %l:',
    timestampFormatter: function (date) {
      return date.toTimeString().replace(/.*(\d{2}:\d{2}:\d{2}).*/, '$1');
    },
    levelFormatter: function (level) {
      return level.toUpperCase();
    },
    nameFormatter: function (name) {
      return name || 'root';
    }
  };

  var loggers = {};

  var apply = function apply(logger, config) {
    if (!logger || !logger.setLevel) {
      throw new TypeError('Argument is not a logger');
    }

    /* eslint-disable vars-on-top */
    var isRoot = !!logger.getLogger;
    var originalFactory = logger.methodFactory;
    var name = logger.name || '';
    var parent = loggers[name] || loggers[''] || defaults;
    /* eslint-enable vars-on-top */

    function methodFactory(methodName, logLevel, loggerName) {
      var originalMethod = originalFactory(methodName, logLevel, loggerName);
      var options = loggers[loggerName || ''];

      var hasTimestamp = options.template.indexOf('%t') !== -1;
      var hasLevel = options.template.indexOf('%l') !== -1;
      var hasName = options.template.indexOf('%n') !== -1;

      return function () {
        var content = options.template;

        var length = arguments.length;
        var args = Array(length);
        var key = 0;
        for (; key < length; key++) {
          args[key] = arguments[key];
        }

        if (!(isRoot && loggers[loggerName])) {
          if (hasTimestamp) content = content.replace(/%t/, options.timestampFormatter(new Date()));
          if (hasLevel) content = content.replace(/%l/, options.levelFormatter(methodName));
          if (hasName) content = content.replace(/%n/, options.nameFormatter(loggerName));

          if (args.length && typeof args[0] === 'string') {
            // concat prefix with first argument to support string substitutions
            args[0] = '' + content + ' ' + args[0];
          } else {
            args.unshift(content);
          }
        }

        originalMethod.apply(undefined, args);
      };
    }

    if (!loggers[name]) {
      logger.methodFactory = methodFactory;
    }
    loggers[name] = merge({}, parent, config);

    logger.setLevel(logger.getLevel());
    return logger;
  };

  var api = {
    apply: apply
  };

  var save;
  if (root) {
    save = root.prefix;
    api.noConflict = function () {
      if (root.prefix === api) {
        root.prefix = save;
      }
      return api;
    };
  }

  return api;
}));