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Jul 2, 2019 in React JS

Q:

What are the different phases of component lifecycle?

1 Answer

Jul 2, 2019

The component lifecycle has three distinct lifecycle phases:

  1. Mounting: The component is ready to mount in the browser DOM. This phase covers initialization from constructor()getDerivedStateFromProps()render(), and componentDidMount() lifecycle methods.

  2. Updating: In this phase, the component get updated in two ways, sending the new props and updating the state either from setState() or forceUpdate(). This phase covers getDerivedStateFromProps()shouldComponentUpdate()render()getSnapshotBeforeUpdate() and componentDidUpdate() lifecycle methods.

  3. Unmounting: In this last phase, the component is not needed and get unmounted from the browser DOM. This phase includes componentWillUnmount() lifecycle method.

It's worth mentioning that React internally has a concept of phases when applying changes to the DOM. They are separated as follows

  1. Render The component will render without any side-effects. This applies for Pure components and in this phase, React can pause, abort, or restart the render.

  2. Pre-commit Before the component actually applies the changes to the DOM, there is a moment that allows React to read from the DOM through the getSnapshotBeforeUpdate().

  3. Commit React works with the DOM and executes the final lifecycles respectively componentDidMount() for mounting, componentDidUpdate() for updating, and componentWillUnmount() for unmounting.

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