Does React Re-render All Components After Every `setState()` Call?

ReactJS: When Does "setState" Trigger a Re-Render?

The Question:

Does React re-render all components and subcomponents every time the setState() method is invoked? If so, why?

The Answer:

By default, yes.

Understanding React's Rendering Process:

When the state of a React component is updated using setState(), the following occurs:

• Virtual DOM Render: React invokes the render() method of the component, resulting in the creation of a new virtual DOM data structure representing the updated component state. This process happens every time setState() is called, regardless of whether the state has actually changed.
• Native DOM Render: React then compares the new virtual DOM with the previous version. If there are any differences, it only updates the parts of the actual (native) DOM that have changed. This minimizes the number of actual DOM manipulations required, optimizing performance.

Why Default Re-Rendering:

The default behavior of always re-rendering ensures that React maintains an accurate representation of the component's state. This prevents potential bugs that could arise from mutating the state in place. However, for efficiency, it's recommended to implement the shouldComponentUpdate() method to optimize re-rendering and improve performance.

Customizing Re-Rendering with "shouldComponentUpdate()":

The shouldComponentUpdate() method can be implemented in a component to determine whether a re-render is necessary based on the new props and state. It returns a boolean value (true or false). By default, this method returns true, which means that the component will always re-render when setState() is called. However, you can override this behavior and implement your own logic to optimize re-rendering only when necessary.

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