code: function isControllerPresentWebVR (component, idPrefix, queryObject) {
    var gamepads;
    var sceneEl = component.el.sceneEl;
    var trackedControlsSystem;
    var filterControllerIndex = queryObject.index || 0;
  
    if (!idPrefix) { return false; }
  
    trackedControlsSystem = sceneEl && sceneEl.systems['tracked-controls-webvr'];
    if (!trackedControlsSystem) { return false; }
  
    gamepads = trackedControlsSystem.controllers;
    if (!gamepads.length) { return false; }
  
    return !!findMatchingControllerWebVR(gamepads, null, idPrefix, queryObject.hand,
                                    filterControllerIndex);
  }
docs: Enumerate controller (that have pose) and check if they match parameters for WebVR
  
  @param {object} component - Tracked controls component.
  @param {object} idPrefix - Prefix to match in gamepad id if any.
  @param {object} queryObject - Map of values to match.