Why componentWillMount should not be used?

Question

Firing server call to fetch data in componentWillMount life cycle method a bad practice?

And why it is better to use componentDidMount.

Answer 1

componentDidMount is the best place to put calls to fetch data, for two reasons:

1. Using componentDidMount makes it clear that data won’t be loaded until after the initial render. You need to setup initial state properly, so you don’t get undefined state that causes errors.

2. If you need to render your app on the server, componentWillMount will be called twice(on the server and again on the client), which is probably not what you want. Putting the data loading code in componentDidMount will ensure that data is only fetched from the client. Generally, you should not add side effects to componentWillMount.