fetch_rest.js

class FetchRest {
  ....
  
  putValue(name, value) {
     // Set value via REST as well as updating the state
    var newParameters = {...this.component.state.api, [parameterName] : value};
    this.component.setState({api: newParameters});
    fetch( this.restServerUrl + '/api/' + name,
      {
        method: 'PUT',
        headers: this.header,
        body: JSON.stringify(value)
      });
  }
  
  

index.js

  handleReset() {
    this.context.apiCallbacks.putValue("gamma", {r:1,g:1,b:1});
    this.context.apiCallbacks.putValue("blackLevel", {r:0.3,g:0.3,b:0.3});
    this.context.apiCallbacks.putValue("whiteLevel", {r:1,g:1,b:1});
  }