Navigation.jsx

import React, { Component } from "react";
import logo from "../images/evli-logo-n.svg";
import '../styles/Navigation.css'

class Navigation extends Component {
  constructor(props) {
    super(props);
    this.ossi = this.ossi.bind(this);
  }

  ossi() {
    fetch('http://localhost:8080/customers', {
      mode: 'cors',
      method: 'POST'
    }).then(resp => {
      return resp.json() // <- Tähän jotain muuta
    }).then(data => {

    }).catch(function(error) {

    });
  }

  render() {
    return (
      <div className="nav">
        <img src={logo} className="evli-logo" alt="logo" />
        <ul>
          <li className='active'>Sopimuksen luonti</li>
          <li>Arkisto</li>
          <li>Asetukset</li>
          <li>Poistu</li>
          <li onClick={() => this.ossi()}>Ossin testinappula</li>
        </ul>
      </div>
    );
  }
}

export default Navigation;