frame-resizer.js

class FrameResizer {
	constructor (frameSelector) {
		this.frameSelector = frameSelector;
		this.iFrame = document.querySelector(this.frameSelector);
		this.iFrameOrigin = new URL(this.iFrame.src).origin;
	}

	_addEvent (element, type, callback) {
		return element.addEventListener(type, callback, false);
	}

	_resizeFrame (event) {
		if (!event.origin.includes(this.iFrameOrigin)) {
			return;
		}

		const height = Number(event.data);
		this.iFrame.height = height;
	}

	notifyResize () {
		this.iFrame.contentWindow.postMessage('resize', '*');
	}

	initialize () {
		this._addEvent(window, 'message', this._resizeFrame.bind(this));
		this._addEvent(window, 'resize', this.notifyResize.bind(this));

		this.notifyResize();
	}
}

window.FrameResizer = FrameResizer;