LifeCycle Methods Replicated with Hooks

LifeCycle Methods Replicated with Hooks

The React tutorial will give some explanation of what each lifecycle method is for, and show how you can replicate similar behaviors using the Hooks API. React’s Hook API has been ever more popular and usable in the front-end world. Go from the class-based component architecture and implement same functionality with much faster and cleaner Hooks API!

For new developers coming from an Object Oriented Programming (OOP) background, classes and lifecycle methods may be much easier to understand. However, React’s Hook API has been ever more popular and usable in the front-end world.

What are Lifecycle Methods?

Here is a chart listing all the lifecycle methods in each phase of the component: mounting, updating, and un-mounting. As you can see, mounting and updating share couple of methods, but the others are very distinct to each step in the lifecycle.

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LifeCycle in Hooks

The rest of the article will give some explanation of what each lifecycle method is for, and show how you can replicate similar behaviors using the Hooks API.


The constructor is a special one for React Components. The fact that React.Componentis a class, we have to extend this class from React for all our components. React hooks work a bit differently: they are not classes, rather functions. Meaning, we do not need a constructor!

However, the point remains: constructor is usually used for setting the initial state of your class based component. You can still set the initial state using the useState Hook:

// useState takes initial state as first argument
const [list, setList] = useState([]);

Or, you can also opt to pass useState a function, which will return your initial state. This can be useful for initial values that depend on some large CPU-intensive computations:

import {getInitialTodoList} from ‘./../data-api’;

// useState can take functions which return your initial state
const [list, setList] = useState(() => getInitialTodoList());


This method is self-explanatory, it runs once when the component is first mounted. It is important to remember that it runs after the render method is completed and the DOM is drawn. If you call an API in this lifecycle method, make sure that you have your loaders set up, otherwise the data will be empty on first-draw.

You can accomplish the same using the useEffect hook. It takes in two arguments: the function to run, and the dependencies to watch. For this use case, we do not want to run this piece of code twice, so we do not have any dependencies.

useEffect(() => {

  // code to run after first render
  const subscription = myTodoObservable.subscribe(() => { … })
}, []) // Empty array means only run this code once after render


The next one you might be wondering is about componentWillUnmount. In this method, you must unsubscribe to any event handlers. The nice thing about Hooks API is the fact that your code is so close together, and it uses closures to refer to variables.

useEffect can return a “clean up” function which will run once the effect is done, as so:

useEffect(() => {
  const subscription = myTodoObservable.subscribe(() => { … })

  // Clean up for “componentWillUnmount”
  return () => {
}, [])


The render method is the most used method, and it’s job is to: render the provided JSX. Since hooks are used in function-based components, we can return our own JSX just like render method. Simply remove the “render” keyword, and return the JSX.

function TodoList() {
  const [list, setList] = useState([]);

  return (
      { =>
        <li key={}>{}</li>}


This one gets a bit tricky, because it is called every single time that the props or the state updates (coming from a parent component or global contexts). componentDidUpdate takes in 3 arguments:

  • prevProps: props from the last render
  • prevState: state from the previous render
  • snapshot: the value from getSnapshotBeforeUpdate which we will talk about next.

The reason you would run this method is because something in your component’s state or props has updated and you need to react to it (pun intended). You can accomplish this same thing by running an “effect” when your prop or state value updates.

Let’s say that you need to call an API whenever your list of todo items reaches a multiple of 5. Usually, you might have some if-else block in componentDidUpdate. Let’s do that using hooks:

function TodoList() {
  const [list, setList] = useState([]);

  // effect to run
  useEffect(() => {
    if (list.length % 5 === 0) {
      // call your API here
  // Our dependency is “list”. Run every time list updates
  }, [list]);

  return (
    <ul>{ => <li key={}>{}</li>}<ul/>

Remember: you can have an indefinite amount of useEffect blocks which have the same or different dependencies. They will run in order from top-to-bottom. Try not to cram all your code into a single useEffect.

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