ReactJs life cycle in brief

If you’re messing around with components…

MOUNTING

getInitialState: Invoked once before the component is mounted. The return value will be used as the initial value of this.state

componentWillMount: Invoked once, both on the client and server, immediately before the initial rendering occurs. If you call setState within this method, render() will see the updated state and will be executed only once despite the state change.

render(): When called, it should examine this.props and this.state and return a single child element. This child element can be either a virtual representation of a native DOM component (such as <div /> or React.DOM.div()) or another composite component that you’ve defined yourself. You can also return null or false to indicate that you don’t want anything rendered. Behind the scenes, React renders a <noscript> tag to work with our current diffing algorithm. When returning null or false, ReactDOM.findDOMNode(this) will return null. The render() function should be pure, meaning that it does not modify component state, it returns the same result each time it’s invoked, and it does not read from or write to the DOM or otherwise interact with the browser (e.g., by using setTimeout). If you need to interact with the browser, perform your work in componentDidMount() or the other lifecycle methods instead. Keeping render() pure makes server rendering more practical and makes components easier to think about.

componentDidMount: Invoked once, only on the client (not on the server), immediately after the initial rendering occurs. At this point in the lifecycle, you can access any refs to your children (e.g., to access the underlying DOM representation). The componentDidMount() method of child components is invoked before that of parent components. If you want to integrate with other JavaScript frameworks, set timers using setTimeout or setInterval, or send AJAX requests, perform those operations in this method.

Updating

componentWillReceiveProps: Invoked when a component is receiving new props. This method is not called for the initial render. Use this as an opportunity to react to a prop transition before render() is called by updating the state using this.setState(). The old props can be accessed via this.props. Calling this.setState() within this function will not trigger an additional render.

shouldComponentUpdate: Invoked before rendering when new props or state are being received. This method is not called for the initial render or when forceUpdate is used. Use this as an opportunity to return false when you’re certain that the transition to the new props and state will not require a component update.

componentWillUpdate: Invoked immediately before rendering when new props or state are being received. This method is not called for the initial render. Use this as an opportunity to perform preparation before an update occurs.

componentDidUpdate: Invoked immediately after the component’s updates are flushed to the DOM. This method is not called for the initial render.
Use this as an opportunity to operate on the DOM when the component has been updated.

Unmounting

componentWillUnmount: Invoked immediately before a component is unmounted from the DOM. Perform any necessary cleanup in this method, such as invalidating timers or cleaning up any DOM elements that were created in componentDidMount.


I hope this brief explanation without code helps. You can get all this information in the documentation but having it in one place like this can be easier to reference for those starting out.