function stateStr(state) {
	    if (state & STATE_CANCELLED) {
	        return 'cancel';
	    } else if (state & STATE_ENDED) {
	        return 'end';
	    } else if (state & STATE_CHANGED) {
	        return 'move';
	    } else if (state & STATE_BEGAN) {
	        return 'start';
	    }
	    return '';
	}
get a usable string, used as event postfix
@param {Const} state
@returns {String} state