Also, the action creator overrides toString() so that the action type becomes its string representation - redux

Question

I'm learning redux-toolkit from the official docs and came across this line- Also, the action creator overrides toString() so that the action type becomes its string representation. What does it mean?
Here's the code from the docs:
const INCREMENT = 'counter/increment'
function increment(amount) {
return {
type: INCREMENT,
payload: amount
}
}
const action = increment(3)
// { type: 'counter/increment', payload: 3 }
const increment = createAction('counter/increment')
let action = increment()
// { type: 'counter/increment' }
action = increment(3)
// returns { type: 'counter/increment', payload: 3 }
console.log(increment.toString())
// 'counter/increment'
console.log(`The action type is: ${increment}`)
// 'The action type is: counter/increment'
So, for example, when I write something like
const increment = createAction("INCREMENT")
console.log(increment.toString())
It's logging INCREMENT. So is this overriding of toString()? I'm really confused.
I'm new to redux-toolkit and any help would be appreciated. Thanks.

Answer 1

Normally, if you call toString() on a function, it returns the literal source text that was used to define the function:
function myFunction() {
const a = 42;
console.log(a);
}
myFunction.toString()
"function myFunction() {
const a = 42;
console.log(a);
}"
However, in this case, we want someActionCreator.toString() to return the action type that will be part of the action objects it creates:
const addTodo = createAction("todos/addTodo");
console.log(addTodo("Buy milk"));
// {type: "todos/addTodo", payload: "Buy milk"}
console.log(addTodo.toString());
// "todos/addTodo"
To make this happen, createAction overrides the actual implementation of toString for these action creators:
export function createAction(type: string): any {
function actionCreator(...args: any[]) {
return { type, payload: args[0] }
}
actionCreator.toString = () => `${type}`
actionCreator.type = type
return actionCreator;
}
This is especially useful because ES6 object literal computed properties automatically try to stringify whatever values you've passed in. So, you can now use an action creator function as the key in an object, and it'll get converted to the type string:
const reducersObject = {
[addTodo]: (state, action) => state.push(action.payload)
}
console.log(reducersObject);
// { "todos/addTodo": Function}