[reactjs] expected assignment or function call: no-unused-expressions ReactJS

import React from 'react';

class Counter extends React.Component{
    state = {
        count: 0,
    };

    formatCount() {
        const {count} = this.state;
        // use a return statement here, it is a importent,
        return count === 0 ? 'Zero' : count;
    }
    render() {
        return(
          <React.Fragment>
              <span>{this.formatCount()}</span>
              <button type="button" className="btn btn-primary">Increment</button>
          </React.Fragment>
        );
    }
}

export default Counter;