JSPM

import {PolymerElement, html} from '@polymer/polymer';
import {mixinBehaviors} from '@polymer/polymer/lib/legacy/class.js';
import {IronA11yKeysBehavior} from '@polymer/iron-a11y-keys-behavior/iron-a11y-keys-behavior.js';

class SampleElement extends  extends mixinBehaviors([IronA11yKeysBehavior], PolymerElement) {
  static get template() {
    return html`
      <pre>[[pressed]]</pre>
    `;
  }

  static get properties() {
    return {
      pressed: {type: String, readOnly: true, value: ''},
      keyBindings: {
        'space': '_onKeydown', // same as 'space:keydown'
        'shift+tab': '_onKeydown',
        'enter:keypress': '_onKeypress',
        'esc:keyup': '_onKeyup'
      }
    }
  }

  function _onKeydown: function(event) {
    console.log(event.detail.combo); // KEY+MODIFIER, e.g. "shift+tab"
    console.log(event.detail.key); // KEY only, e.g. "tab"
    console.log(event.detail.event); // EVENT, e.g. "keydown"
    console.log(event.detail.keyboardEvent); // the original KeyboardEvent
  }
}
customElements.define('sample-element', SampleElement);