Take an action on props change in ReactJS

Question

I need to use current props and previous props value in my React component. So i did it like this

state = {
    current: null,
    previous: null,
};

componentWillReceiveProps(nextProps) {
    if (nextProps.amount !== this.state.current) {
        this.setState({previous: this.state.current, current: nextProps.amount});
    }
}

...

render() {
    const {previous, current} = this.state;

    return (
        ...
        <CountUp className="counter" start={previous} end={current} duration={1}/>
        ...
    )
}

It works fine, but is it good React practise to do it like this? Are there others "good" ways to do it?

Answer 1

As of v16.2.0, componentWillReceiveProps is the right place to update state, based on prop changes and since you want to use both current state and previous state in render, you need to maintain, two different state variables as you are doing

However, when you update the state based on previous state, use functional setState method

Check this answer for more details

When to use functional setState

componentWillReceiveProps(nextProps) {
    if (nextProps.amount !== this.state.current) {
        this.setState(prevState => ({ previous: prevState.current, current: nextProps.amount }));
    }
}

According to the latest RFC to React

State derived from props/state

The purpose of this pattern is to calculate some values derived from props for use during render.

Typically componentWillReceiveProps is used for this, although if the calculation is fast enough it could just be done in render.:

From v16.3.0 onwards, you would make use of

static getDerivedStateFromProps(nextProps, prevState) {
    if (
      !prevState ||
      prevState.current !== nextProps.amount
    ) {
      return {
        previous: prevState.current,
        current: nextProps.amount
      };
    }
}