This is a Babel plugin & macro which adds a straightforward, declarative syntax for adding debug logging to JavaScript applications.

It's common to insert console.log() statements to help keep track of the internal state of functions when writing tricky pieces of code. During development this is very useful, but it creates a lot of noise in the console, and when development of that particular piece of code is complete, the developer is likely to delete the console.log() calls. If we're lucky, they might leave comments in their place.

This is a tragedy - that logging information is extremely useful, not only is it helpful when fixing bugs, it's a great assistance for new developers (including yourself, 6 months from now) when getting to know a codebase.

This plugin repurposes JavaScript LabeledStatements like log: and trace: to provide a logging / tracing syntax which can be selectively enabled or disabled at the folder, file, or function level at build time. Normally, these labels are only used as targets for labeled break and continue statements.

When disabled in production the logging statements are completely dropped out, incurring no overhead. The syntax looks like this:

// login.jsasyncfunctionauthenticate(username,password){ log: 'authenticating user',username;constuser=awaitdb.select().from('users').where({username: username});if(!user){ log: 'no such user';returnfalse;}elseif(!user.checkPassword(password)){ log: ({password: 'invalid'})returnfalse;}elseif(!user.isActive){ log: 'user is not active';returnfalse;} log: 'logging user',username,'into the site';returntrue;}

This will produce output like:

login:authenticate: authenticating user Bob login:authenticate: no such user login:authenticate: authenticating user Alice login:authenticate: invalid password login:authenticate: authenticating user Alice login:authenticate: logging user Alice into the site 

As well as log:, you can also use trace: and warn:, or specify your own using the aliases plugin option. By default all trace: logs will be stripped (unless specifically enabled) and warn: will use console.warn rather than console.log.

Install via npm.

npm install --save-dev babel-plugin-trace 

In your Babel configuration, add "trace" to your list of plugins. The default configuration will strip all logging from production builds, as well as trace logging from development and test environment, corresponding to this configuration:

{"plugins": [ ["trace",{"strip":{"log":{"production": true }, "trace": true, "warn":{"production": true } } }] ] }

"strip" may also take a true value to disable all logging by default. In this case you can still enable it for certain files or functions using environment variables:

{"plugins": [ ["trace",{"strip": true }] ] }

As an alternative to use as a plugin, babel-plugin-trace/macro is provided for use together with babel-plugin-macros. This is relevant in particular if you're working with a create-react-app project, as that does not otherwise allow for Babel plugins to be used. With macro use, you'll need to import the macro in every file where you'd like to enable logging:

importinitTracefrom'babel-plugin-trace/macro'initTrace() log: 'This is',{a: 'message'} warn: ({this: 'a warning'})// parentheses are required if the first value is an{object }

To customise the logging labels, import them as named imports of the macro (the default import is still required, as the labels don't really match the imported variable bindings):

importinitTrace,{log,announce}from'babel-plugin-trace/macro'initTrace() announce: 'This is',{an: 'announcement'} warn: 'This is not logged as a warning'

A source reference to the default export is required to trigger the macro; it will be removed during transpilation.

Log only warn statements.

TRACE_LEVEL=warn babel -d ./lib ./src 

Log trace and warn statements.

TRACE_LEVEL=trace,warn babel -d ./lib ./src 

Enable logging for any file with login.js in the path.

TRACE_FILE=login.js babel -d ./lib ./src 

Enable logging for any file with db/models or components/login in the path.

TRACE_FILE=db/models,components/login babel -d ./lib ./src 

Enable logging for any function called login() or logout().

TRACE_CONTEXT=:login,:logout babel -d ./lib ./src 

Enable logging for any function in a class called User.

TRACE_CONTEXT=:User: babel -d ./lib ./src 

Published by codemix under a permissive MIT License, see LICENSE.md.