Question: I am trying to click on `<GroupsRow />` and have that call a function so I can use the index to change a property. Yet my click never fires `handler()`.

```
export default class GroupsContainer extends React.Component {
  constructor(props) {
   super(props);
  }

  handler(index) {
    console.log(index)
  }

  _repeatGroupRows(tags) {
    return tags.map((tag, index) =>
      <GroupsRow key={index} tag={tag} onClick={this.handler.bind(this, index)} />
    );
  }

  render() {
    return (
      <div className="groups-list-wrapper">
        <GroupsHeader />
        {this._repeatGroupRows(this.props.state.tags)}
      </div>
    );
  }
}

```

Answer: 
You did not post the code for `GroupsRow` component but my guess is that you don't call this handler inside this component.  

`GroupsRow` should call the `props.onClick` handler as it's a react element and not a "normal" DOM element.
The `map` function does not preserve context, so `this` will not be what you expect and `this.handler` will be undefined.

`map` does accept a second argument for this exact purpose though. It should look like this;

```
_repeatGroupRows(tags) {
    return tags.map((tag, index) => {
      return <GroupsRow key={index} tag={tag} onClick={this.handler.bind(this, index)} />
    }, this);
  }

```

EDIT: @lustoykov is correct in his answer that this is not the problem due to the fact that a bind is used. Bit of tunnel vision on my part, as I see a lot of people failing to use both the bind and `thisArg`, but that's not the issue this time!