SVG中的文字

由于svg控制中只有通过text和tspan两个标签进行操作，所以几乎所有的对齐方式都得通过计算来获得，找了很久找到这篇帖子http://bl.ocks.org/MSCAU/58bba77cdcae42fc2f44。

里面介绍了几个很有用的属性可以操作：

1 .getBBox().width

IE and Firefox can't get the BBox of a TSPAN and error out.

2.getBoundingClientRect().width

Integer in IE, Chrome and Safari. Same width as "test1" in Chrome eventhough 2 is wider than 1.

3 .getComputedTextLength()

A TSPAN which is not in a TEXT has no width