redux-log-state-diff

Redux middleware to log actions that change given subsets of state

Ever wonder which action resulted in a change to some part of your Redux state?

Introducing a debugging tool that logs a state diff and action type when specified parts of the state change, according to provided state paths or predicate functions.

logStateDiff(pathsAndPredicates, options)

import logStateDiff from 'redux-log-state-diff'

createStore(
  reducer,
  applyMiddleware(
    logStateDiff([
      'subState.path',
      'otherSubPath.somewhere',
      (prevState, nextState) => prevState.foo !== nextState.foo
    ])
  )
)

Now suppose an action SOME_ACTION_TYPE is dispatched that updates state.subState.path, then the middleware might log:

redux-log-state-diff: action "SOME_ACTION_TYPE", predicate "subState.path" {...a state diff object..}

If you want to be able to control which values are logged at runtime, you could wire up a query parameter:

import { logStateDiffParams } from 'redux-log-state-diff'

createStore(
  reducer,
  applyMiddleware(logStateDiffParams())
)

Then hit your app with a __REDUX_LOG_STATE_DIFF__ query parameter with comma-separated state paths:
https://localhost:8000/my/path?__REDUX_LOG_STATE_DIFF__=subState.path,otherSubPath.somewhere

and it will act as if you had configured with these state paths:

logStateDiff([
  'subState.path',
  'otherSubPath.somewhere',
])

logStateDiffParams accepts the same arguments as logStateDiff - that is, pathsAndPredicates (which will be merged with params-derived ones), and options.