Can't clear form/state after input in React.js

Question

I have a form which ultimately will be used as the UI to make some API calls to Open weather map.

Right now when I submit the a zip code in the input field, upon submission [object Object] propagates the field like in the screen shot below.

The call to the API is working as I am getting the JSON for the correct zip code...

But shouldn't this in the handleSubmit take care of everything i.e. using Object.assign to create new state and then using form.zipcode.value = ''; to clear out the input?

Thanks in advance!!

handleSubmit(event) {
    event.preventDefault();
    var form = document.forms.weatherApp;
    api.getWeatherByZip(this.state.zipcode).then(
      function(zip) {
        console.log('zip', zip);

        this.setState(function() {
          return {
            zipcode: Object.assign({}, zip),
          };
        });
      }.bind(this)
    );
    form.zipcode.value = '';
  }

I have enclosed all of the component's code here.

import React, { Component } from 'react';
    import * as api from '../utils/api';

    import '../scss/app.scss';

    export default class App extends Component {
      constructor(props) {
        super(props);
        this.state = {
          zipcode: [],
        };
        this.handleChange = this.handleChange.bind(this);
        this.handleSubmit = this.handleSubmit.bind(this);
      }

      handleChange(event) {
        this.setState({
          zipcode: event.target.value,
        });
      }

      handleSubmit(event) {
        event.preventDefault();
        var form = document.forms.weatherApp;
        api.getWeatherByZip(this.state.zipcode).then(
          function(zip) {
            console.log('zip', zip);

            this.setState(function() {
              return {
                zipcode: Object.assign({}, zip),
              };
            });
          }.bind(this)
        );
        form.zipcode.value = '';
      }

      render() {
        return (
          <div className="container">
            <form name="weatherApp" onSubmit={this.handleSubmit}>
              <h2>Open Weather App</h2>
              <div className="row">
                <div className="one-half column">
                  <label htmlFor="insertMode">Insert your location</label>
                  <input
                    name="zipcode"
                    className="u-full-width"
                    placeholder="please enter your zipcode"
                    type="text"
                    autoComplete="off"
                    value={this.state.zipcode}
                    onChange={this.handleChange}
                  />
                </div>
                <div className="one-half column">
                  <label htmlFor="showMin">show minimum</label>
                  <input type="checkbox" />
                  <label htmlFor="showMax">show maximum</label>
                  <input type="checkbox" />
                  <label htmlFor="showMean">show mean</label>
                  <input type="checkbox" />
                </div>
              </div>
              <div className="row">
                <div className="two-half column">
                  <input type="submit" value="Submit" />
                </div>
              </div>
            </form>
          </div>
        );
      }
    }

Answer 1

You should let react manage the changes to the DOM rather that editing it manually. As the value of your input field is already bound to this.state.zipcode to reset it just invoke this.setState({zipcode: ''}) instead of form.zipcode.value='';.