useState()

Understanding useState in Modularjs

useState is a fundamental hook provided by Modularjs that allows you to create reactive state inside your modular components. It works similarly to React’s useState and lets you manage data that can change over time, triggering your component to update accordingly.

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What is useState ?

• useState lets you declare a state variable inside your module.

• It returns an array with two values:

  1. The current state value.

  2. A function to update this state.

• When you call the update function, Modularjs re-renders the component with the new state.

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How to use useState

Here is a simple example showing how to use useState to create a counter inside your Modularjs component:

module.exports = ({ useState }) => {
  const [count, setCount] = useState(0);

  return (
    <div>
      <h1>Counter Example</h1>
      <p>Current count: {count}</p>
      <button onClick={() => setCount(count + 1)}>Increment</button>
    </div>
  );
};

Explanation:

• const [count, setCount] = useState(0); Initializes count with the value 0.

• setCount(count + 1) updates the state, causing the component to re-render with the new count.

Here is another simple example showing how to use useState to create a toggle switch inside your Modularjs component:

module.exports = ({ useState }) => {
  const [isOn, setIsOn] = useState(false);

  return (
    <div>
      <h1>Toggle Switch</h1>
      <p>The switch is <strong>{isOn ? 'ON' : 'OFF'}</strong></p>
      <button onClick={() => setIsOn(!isOn)}>
        {isOn ? 'Turn OFF' : 'Turn ON'}
      </button>
    </div>
  );
};

Explanation:

• const [isOn, setIsOn] = useState(false); initializes the toggle state as false (OFF).

• Clicking the button calls setIsOn(!isOn), which flips the boolean value.

• The UI text updates dynamically to reflect the toggle state

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Tips for Using useState

• You can declare multiple state variables for different data in your component.

• Always use the update function (setCount in the example) to change state instead of modifying state variables directly.

• State updates are asynchronous and batched — be mindful when updating state multiple times.

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This page gives you the core knowledge to start building reactive modules with Modularjs using useState!