How to update text element after property change in Polymer 3?

Question

So I'm using a data table which has an active element. When that active elment changes I store the name of the active element in a property of my polymer element. Then I display this String property in a div. Now I know for certain that the property change works, because I console.log it after a change, the div displaying the property doesn't update and continually displays the default value I have set.

export class ProjectsOverview extends PolymerElement {
  static get template() {
      return html`
         ...
         <div>{{currentProject}}</div>
         ...
      `
  }

  static get properties() {
      return {
        currentProject: {
          type: String,
          value: "placeholder",
          notify: true,
          reflectToAttribute: true
        }
      };
  }

  connectedCallback() {
      super.connectedCallback();

      const grid = this.shadowRoot.querySelector('vaadin-grid');

      grid.addEventListener('active-item-changed', function(event) {
        const item = event.detail.value;

        grid.selectedItems = [item];
        if (item) {
          this.set('currentProject', item.name);
        } else {
          this.set('currentProject', '');
        }
        console.log(this.currentProject);
      });
  }
}

My expected result would be that every time the currentProject property is updated, the div displaying the property updates as well.

Answer 1

The active-item-changed callback does not have its context bound to the Polymer instance (i.e., this is the grid and not the Polymer component). Instead of the function expression, use an arrow function to automatically bind this to the correct context.

// grid.addEventListener('active-item-changed', function(event) { // DON'T DO THIS
grid.addEventListener('active-item-changed', (event) => {
  /* this is the Polymer instance here */
  this.set('currentProject', ...);
})