function classSingleAdd(shapeEl, shapeData, classPrefix, classToAdd) {
	if (!shapeData.styles) { shapeData.styles = []; }

	const currentClass = shapeData.styles.findIndex(ss => ss.startsWith(classPrefix));
	if (currentClass > -1) {
		classDel(shapeEl, shapeData.styles[currentClass]);
		shapeData.styles.splice(currentClass, 1);
	}
	shapeData.styles.push(classToAdd);
	classAdd(shapeEl, classToAdd);
}
@param {Element} shapeEl, @param {{styles?:string[]}} shapeData, @param {string} classPrefix, @param {string} classToAdd