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    0.4.1 • Public • Published

    npm version


    A thin wrapper for visionmedia/debug logger, adding levels and colored output.


    visionmedia/debug is a ubitiquous logging library with 1000+ dependants. Given how widespread it is and the convenience of namespaces it is a great logger for library modules. debug-logger is a convenience wrapper around debug that adds level based coloured output. Each instance of debug-logger will lazily instantiate several instances of debug such as namespace:info, namespace:warn, namespace:error, etc. All these are configurable. debug-logger has no dependencies besides debug.

    debug-logger uses the same syntax as node.js console so you can use it as drop in replacement. Check and run examples/console.parity.js for more details.

    At AppsCot we use debug-logger in waterline-orientdb.


    npm install debug-logger -S


    var log = require('debug-logger')('myapp');
    log.trace("I'm a trace output");
    log.debug("I'm a debug output");
    log.log("I'm a log output");"I'm an info output");
    log.warn("I'm a warn output");
    log.error("I'm an error output");


    Inspect error/object

    var err = new Error('error message');
    err.stack = 'the stack\nline2\nline3';
    log.error('Something failed:', err);
    var obj = {
      anumber : 1234,
      astring : 'str',
      adate : new Date(),
      aboolean : true
    };"let's inspect 'obj'", obj);

    inspect error/object

    Original debug instances and enabled property

    log.debug.logger()("the debug instance of debug, using 'myapp:debug' namespace");
    var debug = debugLogger.debug('myapp:visionmedia');
    debug('Nothing tastes better than the original!');
    if (log.debug.enabled()) {
      // This only runs if environment variable DEBUG includes "myapp:debug" namespace
      log.debug("Debug is enabled");


    util.inspect options

    Full util.inspect options available at

    var debugLogger = require('debug-logger');
    debugLogger.inspectOptions = {
      colors : true
    };'By enabling colors we get this nice colored example:', {
      anumber : 1234,
      astring : 'str',
      adate : new Date(),
      aboolean : true


    Customize available log levels

    debugLogger.levels.error.color = debugLogger.colors.magenta;
    debugLogger.levels.error.prefix = 'ERROR ';
    var customColorLog = debugLogger('myapp');
    customColorLog.error("I'm a 'magenta' error output");

    customize log

    Add log levels

    debugLogger.levels.silly = {
      color : debugLogger.colors.magenta,
      prefix : 'SILLY  ',
      namespaceSuffix : ':silly'
    var sillyLog = debugLogger('myapp');
    sillyLog.silly("I'm a silly output");

    add log levels

    Multiple arguments / util.format style

    log.log("Multiple", "arguments", "including", "objects:", { obj: 'obj'}, "makes life easier");
    log.warn("util.format style string: %s, number: %d and json: %j.", "foo", 13, { obj: 'json'});

    multiple arguments

    Measure code execution time

    for (var i = 0; i < 100; i++) {
      var diff = log.timeEnd('setTimeout', 'debug');
      log.trace('log.timeEnd returns diff so it can be reused:', diff);
    }, 262);

    code time

    Inspect object

    log.dir({ foo: { bar: 1 } });
    log.dir({ foo: { bar: 1 } }, { depth: 0 }, 'warn');

    dir inspect

    Assert condition

    log.assert(1 == 0);
    // More elaborate example
    var log = require('..').config({
      levels: { 
        fatal: {
          color : 5,  //magenta
          prefix : '',
          namespaceSuffix : ':fatal',
          level : 6
    log.assert(1 == 0, 'testing %s %d', 'log.assert', 666, 'fatal');


    stderr vs stdout

    By default trace, debug, log and info output to stdout while warn and error output to stderr. This is configurable, example:

    var log = require('debug')('myapp');
    log.trace("goes to stdout!");
    log.debug("goes to stdout!");
    log.log("goes to stdout!");"goes to stdout!");
    log.warn("goes to stderr");
    log.error("goes to stderr");
    // outputting only to stdout
    var stdout = require('debug').config({ levels: { warn: { fd: 1 }, error: { fd: 1 } } })('stdoutapp');
    stdout.warn("goes to stdout!");
    stdout.error("goes to stdout!");

    Filter by log level (instead of namespace)

    export DEBUG_LEVEL=info

    Only info level and above logs will be outputted.

    More examples in the examples folder.


    Instance Methods

    Assuming log is an instance of debug-logger (var log = require('debug-logger')('myapp');).

    log.trace([data][, ...])

    log.debug([data][, ...])

    log.log([data][, ...])[data][, ...])

    log.warn([data][, ...])

    log.error([data][, ...])

    Prints the data prepended by log level. If the terminal supports colors, each level will have a specific color. If an Error is provided, the toString() and call stack will be outputted. If an Object is provided the toString() and util.inspect() will be outputted. Example:

      myapp:debug I'm a debug output +0ms
      myapp:info  I'm an info output +1ms

    This function can take multiple arguments in a printf()-like way, if formatting elements are not found in the first string then util.inspect is used on each argument.

    log([message][, ...])

    Outputs the message using the root/default debug instance, without the level suffix. Example:

      myapp I'm a root/default debug instance output +0ms


    Returns the default debug instance used by level.


    Boolean indicating if level's logger is enabled.


    Mark a time.

    log.timeEnd(label[, level])

    Finish timer, record output. level will determine the logger used to output the result (defaults to 'log'). Return duration in ms.

    log.dir(obj[, options][, level])

    Uses util.inspect on obj and prints resulting string to the appropriate logger. This function bypasses any custom inspect() function on obj. An optional options object may be passed that alters certain aspects of the formatted string. level will determine the logger used to output the result (defaults to 'log').

    log.assert(value[, message][, ...][, level])

    Similar to console.assert(). Additionally it outputs the error using the appropriate logger set by level (defaults to 'error').



    Configures debug-logger. Returns debug-logger to allow chaining operations.


    Returns visionmedia/debug module.


    npm i debug-logger

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    • appscot
    • dmarcelino