How to define css class for list element in React?

Question

I have a list of domains in my UI. Every domain is a button (it can be clicked and get .active css style). The domains names are coming from server, I get them in componentDidMount() method. So I don't know the quantity of future buttons (domains) in component construct moment.

My goal is to change button style on a user click (add .active css class). The first button should be active by default. I can identify buttons by index in array. So my code looks like this:

constructor(props) {
    super(props)
    this.state = {
        domainClasses: {}
    }
}

And in componentDidMount() method:

componentDidMount() {
    this.props.domains.forEach((data, i) => {
        if (i === 0) {
            this.setState({
                ...this.state.domainClasses,
                [i]: `title active`
            });
        } else {
            this.setState({
                ...this.state.titleClasses,
                [i]: `title`
            });
        }
    });
}

I thought that setState() method will add numeric property in state object and then I can manipulate style on button classes. But it doesn't! I tested - if state doesn't contain numeric property in component construct moment it will ignore it in setState in future.

To resole it I could add every numeric property to state object in constructor method in forEach cycle but I don't know the quantity of domains until they come from server in componentDidMount...

So, my question is - how to change css classes on button click if this buttons in list and the quantity is undefined until server response?

Any help, please!

Yongzhi · Accepted Answer · 2018-12-19 22:16:07Z

1

You are storing a possible huge state for just setting the active class for a button, why not just use something simple like activeButtonIdx

in constructor, your init state will be

this.state = {
  activeButtonIdx : 0
}

Inside ur render function, you can just give the class (Assume it is inside a map since you mentioned that you have a list of buttons)

{
  buttons.map((d, i) => <Button className={this.state.activeButtonIdx === i ? 'active title' : 'title' } onClick={() => this.setState({activeButtonIndex : i})} key={d.id}/>)
}

answered Dec 19, 2018 at 22:16

Yongzhi

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