​why does this code give me an array of undefined when i do console.log(this.itemToSend); ?

element: Element = {

    linkId: '',

    text: '',

    elem: [{

      valueString: '',

    }]

};







  itemToSend: {

    resourceType: string;

    extension: [

      {

        url: string;

        valueCode: string;

      },

      {

        url: string;

        valueDateTime: string;

      }

    ],

    status: string;

    subject: {

      reference: string;

      display: string;

    },

    authored: string;

    elements: any [];

  };



items: Item [];



  item: Item = {

    linkId: '',

    text: '',

    answer: ''

  };



onSend() {

    this.itemToSend = {

      resourceType: 'QuestionnaireResponse',

      extension: [

        {

          url: '',

          valueCode: 'Demetre Vasia'

        },

        {

          url: '',

          valueDateTime: '2018-09-12T04:00:00.000Z'

        }

      ],

      status: 'completed',

      subject: {

        reference: '',

        display: 'Demetre Vasia'

      },

      authored: '2018-11-08T15:41:00.581+00:00',

      elements: []

    };



this.itemToSend.elements = this.items.map(el => {

      this.element.elem[0].valueString = el.answer;

    console.log(this.element.elem[0].valueString);



  });