How to set console log level?

[retog]

I assumed that setting the log-level to info would prevent messages passed to console.debug from appearing, however this doesn't seem to be the case:

$ echo 'console.debug("hi") ' | deno -L info run -
hi

Is there away to have only messages passed to console.info but not those passed to console.debug?

[kitsonk]

deno -L flag is for internal logging of Deno. console.* is for userland code. We should make it clearer in the help what logging it applies to.

console.* behaves a lot like it does in a browser. In a browser, console.log(), console.info(), console.warn(), console.error() change the "display" of the errors and advanced GUI allow filtering, but browsers do not allow "out of the box" suppression, nor does Node.js. Node.js and Deno both send console.error() and console.warn() to stderr instead of stdout.

Adding out of the box suppression would be "surprising" to the established de facto precedent established.

Because the primitive logging is often not sufficient for a lot of workloads, people tend to use a logging framework. There is a logging framework as part of std library, but I think the larger community is split on its usefulness. There are other logging frameworks available on deno.land/x that might be suitable as well.

If you are dealing with 3rd part code, then you might want to consider either patching the global console yourself, or use a package that helps you do that.

In the end, Deno treats console.* as a userland construct/API and doesn't interfere with it.

[retog]

Thanks @kitsonk.

As you mention some GUIs allow filtering, isn't that the whole point of differentiating the log levels? How can a user of the command-line deno tools benefit from the debug/info distinction the developer made? Even in VSCode I see no way to filter the log-level.

I've been using the logging framework in std, but his has the big disadvantage that I don't have links to the relevant line in the source code, when looking at the log output in the browser tools or in VSCode. Also, for my needs, the js standard log API exposed by console is enough.

[SadiePi]

I figured I'd share my workaround if anyone else comes here disappointed. You could search and replace the different levels project wide, like console.debug->//console.debug, to enable and disable different levels. It would still be much better to have an enum value you can set on the console object though.

[mxcl]

this is a fine suggestion! an alternative people may like is: console.debug = () => {}

[jupegarnica]

We really need a console.setLevel() method in the standard. And stop using third party libraries for such a basic use case.
@lucacasonato do you know if there is something like this in the oven already?

I am dreaming for years with it

[luolong]

Browser UI allows filtering of output based on log levels.

I'd say, adding command line argument to have similar filtering in the CLI application makes a wolrd of sense.

[bartlomieju]

I think we could add a flag that allows filtering. Before we do that, an issue with proposed flag name should be opened and agreed upon.

[jcayzac]

Right now, .debug(), .info() and .log() send to 1 (stdout) while .warn() and .error() send to 2 (stderr), and while they make sense they are arbitrary.

Letting us specify an append-only destination for each level on the command line, being a file handle number or an actual file path, wouldn't do any suppression by itself but offer more flexibility. People could also choose to suppress by sending those logs to /dev/null. Invoked from Bash, this would even let you stream logs over the network directly (using Bash's builtin network support).