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A wrapper around goog.log inspired by pedestal.log.

For more info see the accompanying blog post: ClojureScript logging with goog.log, and Logging in Practice with Glögi and Pedestal.


WARNING: There are two packages with different artefact IDs published on clojars. One is com.lambdaisland/glogi and another is lambdaisland/glogi (without the com.). Please migrate your dependency to com.lambdaisland/glogi as this is the only one which recieves new updates. We apologise for this confusion, but we had to make some changes to stay in accordance with the clojars policy.


com.lambdaisland/glogi {:mvn/version "1.3.169"}


[com.lambdaisland/glogi "1.3.169"]


It is recommended to initialize Glögi at the top of your main namespace, so that no log messages are lost.

  (:require [lambdaisland.glogi :as log]
            [lambdaisland.glogi.console :as glogi-console]))


  {:glogi/root   :info    ;; Set a root logger level, this will be inherited by all loggers
   ' :trace   ;; Some namespaces you might want detailed logging
   ' :error   ;; or for others you only want to see errors.

(log/info :hello {:message "Hello, world!"})

Result in your browser console (but pretty with colors):

[] {:hello {:message "Hello, world!"}}

Before you can start logging you need to install a handler that knows where to output the log messages (browser console, in a div, ...). (glogi-console/install!) is recommended. It contains some smarts so that your Clojure data is logged nicely. When cljs-devtools is active then it will pass data structures unchanged to js/console.log so devtools can render them. If not then it will stringify and colorize them so you get pretty EDN in your console, instead of seeing the implementation details of ClojureScript persistent data structures.

Log functions take key/value pairs.

Loggers and log levels

In goog.log, which glogi is based on, loggers have hierarchical names, with segments separated by dots. If you use Glogi's logging macros then it will automatically get the logger based on the namespace name.

When you call a logging function it will check the log level of the logger to decide if the message should be output ot not. To find this level the logger will go up the hierarchy until it finds a logger with an explicit level set. This is usually the root logger, but it doesn't have to be.

So say you have these namespaces:

You can set the level for individual namespaces

(log/set-levels '{ :debug

But you can also set the level for a subtree of namespaces. So say you're debugging the API, which uses some.lib.

(log/set-levels '{ :all
                  some.lib :debug

This is really convenient and powerful. By sprinkling your code with logging at various levels you can easily get insight in what a particular part is doing, on demand.

Instead of adding more and more print statements as you debug, and then deleting them afterwards, you can add increasingly detailed levels of logging instead. Later when you find yourself in the same waters you can dial the verbosity up or down as you see fit.

Glogi is based on goog.log, and so it understand the log levels that goog.log provides. Glogi also aims to be at least partially API compatible with pedestal.log, and so we provide extra log levels that internally map to goog.log levels.

pedestal goog.log value description
:off Infinity Special value to disable logging
:shout 1200 Critical error
:error :severe 1000 Serious failure
:warn :warning 900 Potential problem, but program continues
:info :info 800 Informational message, e.g. to make background tasks visible
:config 700 Configuration info
:debug :fine 500 Step-by-step debug messages
:trace :finer 400 More verbose, detailed tracing messages
:finest 300 Highly verbose and detailed tracing
:all 0 Special value to show all log messages

There are also two special levels, :all and :off, which you can use in set-levels to turn logging up to the maximum, or turn it off instead.

It is recommended to use a consistent set of logging methods, for instance to use only the pedestal version, possibly augmented by the goog.log levels that don't have a pedestal equivalent.

for instance:

(log/shout ,,,)
(log/severe ,,,)
(log/error ,,,)
(log/warn ,,,)
(log/info ,,,)
(log/config ,,,)
(log/debug ,,,)
(log/trace ,,,)
(log/finest ,,,)

If you are using lambdaisland.glogi.console, then these levels will also influence with js/console method is used, as well as the color used to print the namespace name.


There is a convenience macro spy which you can use to have a quick look at a value. It outputs the form, the value, and returns the value so you can simply wrap any expression you want to see the value. Spy expressions are logged at the :debug level.

(let [x (spy (+ 1 1))
      y (spy (+ x x))]
  (+ x y))
;;=> 6
[my.ns] {:spy (+ 1 1) :=> 2}
[my.ns] {:spy (+ x x) :=> 4}

As you may have noticed, unlike js/console.log or prn, spy returns the value of the expression so you can wrap expressions with it without disrupting the flow of your program.

If you pass multiple values to spy, all will be printed:

(fn [{:keys [host port path protocol] :as config}]
  (spy host port)
[my.ns] {:spy [host "localhost" port 8080]}

This will be logged slighly diferently on Clojure. This is because Pedestal doesn't directly support multiple values to spy, and Glogc tries to be a thin wrapper:

[my.ns] {:spy [host port] :value ["localhost" 8080]}

If you call spy on multiple values, the last value will be returned, analogous to do.

Special keys

Two keywords have a special meaning in logging calls.

  • :exception use this if you want to log an exception, this will make sure you get a proper stacktrace in the browser console
  • :lambdaisland.glogi/logger name of the logger to use, defaults to (str *ns*)

Controlling colorization

When using lambdaisland.glogi.console/install! it will try to detect what the best logging strategy is for your environment.

  • if cljs-devtools is detected then it will log ClojureScript objects directly
  • if it detects a browser that is not pre-chromium IE/Edge, then it will use console.log "%c" CSS-based colorization
  • all other cases it logs plain text

This behaviour can be changed by setting lambdaisland.glogi.console.colorize in :closure-defines in your compiler options.

  • "auto" the autodetect behavior described above (default)
  • "raw" always log ClojureScript objects directly
  • "true" format using CSS
  • "false" format as plain text

Logging in production

Production builds typically have goog.DEBUG set to false. This strips out some development checks, it also strips out logging. If you still want to see logs on production then add this to your ClojureScript compiler options:

:closure-defines {goog.DEBUG false
                  goog.debug.LOGGING_ENABLED true}

Use with Pedestal

The lambdaisland.glogc namespace provides a cross-platform (cljc) API, which uses Glogi on ClojureScript, and io.pedestal.log on Clojure. This way it's easy to do logging from cljc code, or just to have a consistent logging setup without having to wonder what kind of file you are in.

Note that the pedestal.log dependency is "BYO" (bring your own), you need to add it explicitly to your dependencies.

(ns my.ns
  (:require [lambdaisland.glogc :as log))

(log/debug :foo :bar)

goog.log has more distinct log levels than Pedestal. We provide macros for all of them, on Clojure they simply map to the nearest equivalent.

  • finest -> trace
  • finer -> trace
  • fine -> debug
  • config -> info

Supported by Nextjournal

Many thanks to Nextjournal for coming up with an interesting problem, and giving me the opportunity to explore and solve it.

Lambda Island Open Source


glogi is part of a growing collection of quality Clojure libraries created and maintained by the fine folks at Gaiwan.

Pay it forward by becoming a backer on our Open Collective, so that we may continue to enjoy a thriving Clojure ecosystem.

You can find an overview of our projects at lambdaisland/open-source.




Everyone has a right to submit patches to glogi, and thus become a contributor.

Contributors MUST

  • adhere to the LambdaIsland Clojure Style Guide
  • write patches that solve a problem. Start by stating the problem, then supply a minimal solution. *
  • agree to license their contributions as MPL 2.0.
  • not break the contract with downstream consumers. **
  • not break the tests.

Contributors SHOULD

  • update the CHANGELOG and README.
  • add tests for new functionality.

If you submit a pull request that adheres to these rules, then it will almost certainly be merged immediately. However some things may require more consideration. If you add new dependencies, or significantly increase the API surface, then we need to decide if these changes are in line with the project's goals. In this case you can start by writing a pitch, and collecting feedback on it.

* This goes for features too, a feature needs to solve a problem. State the problem it solves, then supply a minimal solution.

** As long as this project has not seen a public release (i.e. is not on Clojars) we may still consider making breaking changes, if there is consensus that the changes are justified.


Copyright © 2019-2021 Arne Brasseur and Contributors

Licensed under the term of the Mozilla Public License 2.0, see LICENSE.