example.tsx

import React, { Component } from 'react';

type Day = {
  dayText : string;
}

type Props = { }

type State = {
  days : Day[]
}

function dayToClassNames(day : Day) {
    return day.dayText;
}

class Foo extends Component<Props, State> {
    handleDayClick(day : Day) {
        return () => {
          console.log(day);
        };
    }
    render() {
        const { days } = this.state;
        return <div>
            {days.map((day, dayIndex) =>
                <td key={dayIndex}>
                    className={dayToClassNames(day)}
                    onClick={this.handleDayClick(day)}
                >
                  {day.dayText}
                </td>
            )}
        </div>
    }
}