React Lifecycle Methods

Phases

1. Initialisation
2. Mounting
3. Updating
4. Unmounting

1. Initialisation
Setting up of initial state and default props happen here.
  a. constructor
    - Constructor is called during initialisation.

2. Mounting
 a. componentWillMount
   - Executed just before the React component is about to mount in the DOM. Executed once before 1st render
 b. componentDidMount
   - Executed after the component is mounted in the DOM.
 NOTE: API calls should be made in componentDidMount
 
3. Updating
  a. shouldComponentUpdate
    - Method should return `true` or `false` and if `true` the component's render method is called. Not required most of the times unless we're dealing with a heavy component that can have performance bottlenecks.
    - React.PureComponent always does a shallow copy before deciding whether component should be updated
  b. componentWillUpdate
    - Executed only after `shouldComponentUpdate` returns `true`. Used to prepare for upcoming render.
  c. componentDidUpdate
    - Executed after the new update is rendered in the DOM.
  
  Below methods are called when parent sends new props:
  a. componentWillReceiveProps
    - Gets executed when props have changed and it's not the first render.
    
4. Unmounting
  a. componentWillUnmount
    - Last method in the lifecycle. Executed just before component is removed from the DOM. Used mainly for cleanup.