ReactJS Form Submit keeps causing refresh of page

Question

Learning basics of react here.

I have a simple Zipcode form I'm trying to update the Zipcode in the form component I made and in the app parent component I made.

In my onSumbit prop I call a function to update and added e.preventDefault();

but the submit button still refreshes everything and i'm pretty sure loses my data.

I commented out my onInput functions and props because I realize it's not affecting my onSubmit action but let me know if that's needed in React for some reason.

I can add more if needed. In my index I am using bootstrap4 cdn

App.js:

   import React, { Component } from 'react';
import GMap from './GMap';
import ZipCode from './ZipCode';
import './css/App.css';

class App extends Component {
  constructor(props){
    super(props);
    this.state = {zipcode : ''};
    this.onZipCodeChange = this.onZipCodeChange.bind(this);
  }

  onZipCodeChange(e){
    e.preventDefault();
    console.log('App has detected ZipCode Change');
    const value = e.target;
    this.setState({zipcode: value});
  }

  render() {
    return (
      <div className="App">
        <header>
          <nav className="navbar navbar-expand-lg navbar-light bg-light">
            <a className="navbar-brand" href="#">Navbar</a>
            <button className="navbar-toggler" type="button" data-toggle="collapse" data-target="#navbarNav" aria-controls="navbarNav" aria-expanded="false" aria-label="Toggle navigation">
              <span className="navbar-toggler-icon"></span>
            </button>
            <div className="collapse navbar-collapse" id="navbarNav">
              <ul className="navbar-nav">
                <li className="nav-item active">
                  <a className="nav-link" href="#">Home <span className="sr-only">(current)</span></a>
                </li>
                <li className="nav-item">
                  <a className="nav-link" href="#">Features</a>
                </li>
                <li className="nav-item">
                  <a className="nav-link" href="#">Pricing</a>
                </li>
                <li className="nav-item">
                  <a className="nav-link disabled" href="#">Disabled</a>
                </li>
              </ul>
            </div>
          </nav>
        </header>
          <ZipCode onSubmit={this.onZipCodeChange}  />
          <GMap />
      </div>
    );
  }
}

export default App;

ZipCode.js:

import React, { Component } from 'react';
import './css/App.css';


class ZipCode extends Component {
  constructor(props) {
      super(props);
      this.state = {zipcode: ''};
    //  this.updateZip = this.updateZip.bind(this);
      this.submitZipCode = this.submitZipCode.bind(this);
    }
    componentDidMount() {
      console.log(" ZipCode will mount");
  }

  componentWillUnmount() {
    console.log("ZipCode will unmount");
  }

  submitZipCode(e){
    e.preventDefault();
    const { value } = this.state;
    this.setState({zipcode: value});
    const { onSubmit } = this.props; //pull out to call method it is linked to
    console.log('submitting zipcode');
    onSubmit(value);
  }

  // updateZip(e){
  //   const value = e.target;
  //   this.setState({ zipcode : value });
  //   console.log('zipcode updated to: '+ this.state.zipcode.value);
  // }
  //  onInput={this.updateZip}

  render(){
    return(
      <div className="row">
        <div className="col-sm-4 col-md-4 col-lg-4">
          <form onSubmit={this.submitZipCode}>
            <label>Zip Code</label>
            <input
              type="input"
              name="zipcode"
              value={this.zipcode}
             />
            <button type="submit" className='btn btn-success'>Submit</button>
          </form>
          </div>
      </div>
    );
  }
}

export default ZipCode;