JS Practice — Built-in Objects

Selector Functions

📖 Usage Example

function getCounter(state) { return state.counter }
function getUsername(state) { return state.user.name }

// In a component:
const count = getCounter(store.getState())
const name  = getUsername(store.getState())

Selectors decouple components from the shape of the state tree, making refactoring easier.

Selector Functions

Selectors are plain functions that extract a specific piece of data from the Redux state tree:

function getCounter(state) { return state.counter }
function getUser(state) { return state.user }

They centralise access to state shape, so if you rename a key you only update the selector — not every component that reads it.

Challenge: Implement three selectors:

getCounter(state) → state.counter
getUser(state) → state.user
getUsername(state) → state.user.name

💡 Hints (2)

• A selector is just a function: `function getCounter(state) { return state.counter }`.
• Keeping selectors in one place means renaming a state key only requires updating the selector.