function validateSize(height, width) {
	if (height) {
		// if height was user-supplied
		height = Number(height);
		if (isNaN(height)) {
			// input must be a number
			throw Error('height must be a number');
		} else if (height <= 0) {
			throw Error('height must be a positive number');
		}
	} else {
		height = 15;
	}

	if (width) {
		// if width was user-supplied
		width = Number(width);
		if (isNaN(width)) {
			// input must be a number
			throw Error('width must be a number');
		} else if (width <= 0) {
			throw Error('width must be a positive number');
		}
	} else {
		width = 50;
	}

	return { height, width };
}
validateSize
@param {number} height
@param {number} width
@returns {{height: number, width: number}}