Debugging
In basic apps, console.log
can be our best friend for debugging atoms, but when applications get bigger and we have more atoms to use, logging would not be a good way of debugging atoms.
Jotai provides two ways of debugging atoms, React Dev Tools and Redux Dev tools. For reading values and simple debugging, React Dev Tools might suit you, but for more complicated tasks like Time-travelling and setting values, Redux Dev Tools would be a better option.
Debug labels
It is worth mentioning that we have a concept called Debug labels in Jotai which may help us with debugging.
By default each Jotai state has the label like 1:<no debugLabel>
with number being internal key
assigned to each atom automatically. But you can add labels to atoms to help you distinguish them more easily with debugLabel
.
const countAtom = atom(0)// countAtom's debugLabel by default is 'atom1'if (process.env.NODE_ENV !== 'production') {countAtom.debugLabel = 'count'// debugLabel is 'count' now}
Jotai provides both a Babel and a SWC plugin, that adds a debugLabel automatically to every atom, which makes things easier for us. For more info, check out jotai/babel and @swc-jotai/debug-label
Using React Dev Tools
You can use React Dev Tools
to inspect Jotai state. To achieve that useDebugValue
is used inside custom hooks. Keep in mind that it only works in dev mode
(such as NODE_ENV === 'development'
).
useAtom
useAtom
calls useDebugValue
for atom values, so if you select the component that consumes Jotai atoms in React Dev Tools, you would see "Atom" hooks for each atom that is used in the component along with the value it has right now.
useAtomsDebugValue
useAtomsDebugValue
catches all atoms in a component tree under Provider (or an entire tree for Provider-less mode), and useDebugValue
for all atoms values.
If you navigate to the component that has useAtomsDebugValue
in the React Dev Tools, we can see a custom hook "AtomsDebugValue" which allows you to see all atom values and their dependents.
One use case is to put the hook just under the Provider
component:
const DebugAtoms = () => {useAtomsDebugValue()return null}const Root = () => (<Provider><DebugAtoms /><App /></Provider>)
Using Redux DevTools
You can also use Redux DevTools to inspect atoms, with many features like Time-travelling and value dispatching.
useAtomDevtools
useAtomDevtools
is a React hook that manages ReduxDevTools extension for a particular atom.
If you have a specific atom in mind that you may want to debug, useAtomDevtools
can be a good option.
const countAtom = atom(0)// setting countAtom.debugLabel is recommended if we have more atomsfunction Counter() {const [count, setCount] = useAtom(countAtom)useAtomDevtools(countAtom)}
Now if we try setCount
, we can see that the Redux Dev Tools logs those changes immediately.
Time travel
Sometimes we need to switch to a specific value of our atoms' state, with Time travelling this is possible. You can hover on each action you see in the devtools and see the Jump option there, with clicking it you'd be able to switch to that specific value.
Pause
If we don't record changes on atoms, we can stop watching those using the Pausing feature.
Dispatch
It's possible to set values on atoms with the Dispatch feature. You can do that by clicking on the Show Dispatcher button.
This would set the countAtoms
's value to 5
.
We should note that the value will be parsed by JSON.parse, so pass supported values.
useAtomsDevtools
useAtomsDevtools
is a catch-all version ofuseAtomDevtools
where it shows all atoms in the store instead of showing a specific one.
We'd recommend this hook if you want to keep track of all of your atoms in one place. It means every action on every atom that is placed in the bottom of this hook (in the React tree) will be catched by the Redux Dev Tools.
Every feature of useAtomDevtools
is supported in this hook, but there's an extra feature, which includes giving more information about atoms dependents like:
{"values": {"atom1:count": 0,"atom2:doubleCount": 0,"atom3:half": 0,"atom4:sum": 0},"dependents": {"atom1:count": ["atom1:count", "atom2:doubleCount", "atom4:sum"],"atom2:doubleCount": ["atom3:half", "atom4:sum"],"atom3:half": ["atom4:sum"],"atom4:sum": []}}
Frozen Atoms
To find bugs where you accidentally tried to mutate objects stored in atoms you
could use freezeAtom
or freezeAtomCreator
from jotai/utils
bundle.
Which returns atoms value that is deeply freezed with Object.freeze
.
freezeAtom
freezeAtom(anAtom): AtomType
freezeAtom
takes an existing atom and make it "frozen".
It returns the same atom.
The atom value will be deeply frozen by Object.freeze
.
It is useful to find bugs where you unintentionally tried
to change objects (states) which can lead to unexpected behavior.
You may use freezeAtom
with all atoms to prevent this situation.
Parameters
anAtom (required): An atom you wish to freeze.
Examples
import { atom } from 'jotai'import { freezeAtom } from 'jotai/utils'const objAtom = freezeAtom(atom({ count: 0 }))
freezeAtomCreator
If you need, you can define a factory for freezeAtom
.
import { freezeAtom } from 'jotai/utils'export function freezeAtomCreator<CreateAtom extends (...args: unknown[]) => Atom<unknown>,>(createAtom: CreateAtom): CreateAtom {return ((...args: unknown[]) => freezeAtom(createAtom(...args))) as never}