forewarn

Scoped and styled warning logger. Best used sparingly, forewarn writes a message to console unless a condition is falsy or NODE_ENV is production. It's meant to advise consumers of your module when some argument is invalid, but you have an alternative code path to follow. Meaning: instead of throwing an error and breaking the flow, you adapt, and through forewarn, you help developers prevent the situation in the future.

about

This module is adapted from React's warning function:

Similar to invariant but only logs a warning if the condition is not met. This can be used to log issues in development environments in critical paths. Removing the logging code for production environments will keep the same logic and follow the same code paths.

Differences from React's warning:

• Scoped like debug
• The warning message is styled if the execution environment is Chrome, Electron, Firefox with Firebug or Node.js
• The condition argument has flipped polarity and is made explicit (because it's easier to read IMHO):
  • warn.when(3 !== 3, 'Three should be three') reads as "warn if 3 does not equal 3"
  • warn('Three should be three') always warns.
• Arguments are passed to console.warn as is, so you can use all modifiers (depending on environment) instead of just %s and an arbitrary number of extra arguments.

example

const warn = require('forewarn')('my-module')

let path = ['a', 'b']
  , length = path.length
  , minimum = 3

warn.when( length < minimum
         ,'Ignoring invalid path %o because length %d is less than %d'
         , path, length, minimum )

api

warn = forewarn(scope)

Create a warn function. Messages will be prefixed with the string scope (usually the name of your module). Returns a noop in production.

warn(format, ...args)

Log a warning.

warn.when(condition, format, ...args)

Log a warning if condition is truthy.

install

With npm do:

npm install forewarn

license

MIT © Vincent Weevers