If you change the accepted answer's match() pattern to this it adds support for negative numbers:
$(el).css('-webkit-transform').match(/matrix(?:(3d)(-{0,1}d+(?:, -{0,1}d+)*(?:, (-{0,1}d+))(?:, (-{0,1}d+))(?:, (-{0,1}d+)), -{0,1}d+)|(-{0,1}d+(?:, -{0,1}d+)*(?:, (-{0,1}d+))(?:, (-{0,1}d+))))/)
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…