select all

<select value={this.state.value} onChange={this.handleChange}>
    <option value="all">-- all --</option>
    {this.state.events.map((event, index) => (
            <option value={event.summary}>{event.summary}</option>
    ))}
</select>

handleChange = event => {
    let items = this.state.events;
    items = items.filter(item => {
        return event.target.value == "all" || item.summary.toLowerCase().search(event.target.value.toLowerCase()) !== -1;
    });
    this.setState({ items: items, filteredEvents: items });
};