How to use the webvr-polyfill/src/util.isIOS function in webvr-polyfill

function handleTouchMoveRotate( event ) {

        console.log( 'handleTouchMoveRotate' );



        rotateEnd.set(event.touches[0].pageX, event.touches[0].pageY);
        rotateDelta.subVectors(rotateEnd, rotateStart);
        rotateStart.copy(rotateEnd);

        // On iOS, direction is inverted.
        if (Util.isIOS()) {
            //rotateDelta.x *= -1;
        }

        var orientation = scope.orientation;

        var element = scope.domElement === document ? scope.domElement.body : scope.domElement;
        orientation.x += 2 * Math.PI * rotateDelta.y / element.clientWidth * scope.rotateSpeed;

        orientation.y += 2 * Math.PI * rotateDelta.x / element.clientWidth * scope.rotateSpeed;

        //orientation.x = Math.max( - PI_2, Math.min( PI_2, orientation.x ) );

        scope.update();

    }

this.deviceMotion = new DeviceMotion();

		this.accelerometer = new MathUtil.Vector3();
		this.gyroscope = new MathUtil.Vector3();

		this._onDeviceMotionChange = this._onDeviceMotionChange.bind(this);
		this._onScreenOrientationChange = this._onScreenOrientationChange.bind(this);

		this.filter = new ComplementaryFilter(K_FILTER);
		this.posePredictor = new PosePredictor(PREDICTION_TIME_S);

		this.filterToWorldQ = new MathUtil.Quaternion();

		this.isFirefoxAndroid = Util.isFirefoxAndroid();
		this.isIOS = Util.isIOS();

		// Ref https://github.com/immersive-web/cardboard-vr-display/issues/18
		this.isChromeUsingDegrees = agentInfo.browser.name === "chrome" &&
			parseInt(agentInfo.browser.version, 10) >= 66;

		this._isEnabled = false;

		// Set the filter to world transform, depending on OS.
		if (this.isIOS) {
			this.filterToWorldQ.setFromAxisAngle(new MathUtil.Vector3(1, 0, 0), Math.PI / 2);
		} else {
			this.filterToWorldQ.setFromAxisAngle(new MathUtil.Vector3(1, 0, 0), -Math.PI / 2);
		}

		this.inverseWorldToScreenQ = new MathUtil.Quaternion();
		this.worldToScreenQ = new MathUtil.Quaternion();