2021 02 13

Read some more Full-stack React , TS & Node. Learning about React lifecycle methods in class components

• When a component is mounting we have access to the follow methods:

  • constructor the class contructor used for initalising state
  • getDerivedStateFromProps , used for basing state on prop from a parent component. Use carefully as can cause re-renders
  • render used to render out JSX
  • componentDidMount, happens after a component has initialised . A good place for API calls.
  • UNSAFE_componentWillMount, as the methods implies, legacy method. Avoid!

• when a component is updating, we have access to the following methods:

  • shouldComponentUpdate, used to decide if a re-redner should happen or not.
  • getSnapshotBeforeUpdate, capture the state of the dom before a render happens. Usually used alongside componentDidUpdate
  • componentDidUpdate, run immediately after a re-render completes. Can make additional changes to the dom here, or after state. Important to have an exit condition so you dont create an infinite loop.

• when a component is unmounting, we have access to the following methods:

  • componentWillUnmount, used for cleanup work like removing event listeners or subscriptions

• Tap into these lifecyles to help control re-renders. If re-renders get out of controls, the UX will suffer.

• React team recommendations:

  • componentDidUpdate is useful for triggering behaviour based on a prop change.
  • React.memo can control re-renders only when a prop has changed instead of when the parent changes.
  • Make your component fully controlled, so it has no state of it’s own. this usually means drilling a prop down many components deeps which can be annoying.
  • use componentDidMount for rendering state based on an API call. Note componentDidMount only ever runs just once.
  • ComponentDidUpdateis useful for managing state based on prop changes. But generally try to avoid using derived state. Try to just use props directly and have state managed from a parent component.