React ComponentWillMount

// Do a REST Query to get data from REST using spHttpClient
public componentWillMount()
{
    const items: any = await this.props.context.spHttpClient.get(restApi, SPHttpClient.configurations.v1, {
        headers: {
          'Accept': 'application/json;odata.metadata=none'
        }
      }).then(resp => resp.json());
}