Basic visualization of how React useState works (passing parameters to a callback function) (useful for custom hooks)

setState.ts

// https://www.typescriptlang.org/play?#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

function isFunction(functionToCheck: unknown) {
    return functionToCheck && {}.toString.call(functionToCheck) === '[object Function]';
}

let currentState: any;

function _setState(newValue: any) {
    if (isFunction(newValue)) {
        currentState = newValue(currentState)
    } else {
        currentState = newValue
    }
}

function useState<S>(initialValue: S) {
    currentState = initialValue

    return [currentState, _setState] as const
}

const [state, setState] = useState(false)

setState((prev: boolean) => !prev)

console.log(currentState) // too lazy to make state work but you get the idea