constructor function

fetchForLater().then( resp => {

      if ( !resp.ok ) { throw new Error( "Failed to fetch for later people" ); }
      return resp.json();

    } ).then( json => {

      const savedForLater = json.map( ( [ id, person ] ) => person );
      this.setState( { saved: savedForLater } );

    } );

handleSaved function

saveForLater( person ).then( resp => {

      if ( !resp.ok ) {

        throw new Error( "Failed to save person for later" );

      }

    } ).then( () => {

      const saved = this.state.saved;
      saved.push( person );
      this.setState( { saved } );

    } ).catch( err => {

      alert( err.message );

    } );