1. might (just) as well do sth.   用来表示“建议”，意思是“还是做某事好；倒不如做某事”。比 may (just) as well do sth. 更婉转一些。

2. might (just) as well have done sth.  表示“对过去情况的推测”，意思是“好像做了某事；简直做了某事”，两个意思任选其一。

3. as far as his knowledge, or recognition, of his surroundings went：as far as 看作词组连词，意思是“就......而言”。它由   as far as + 主语 + go  构成。这里， go 是引申义，指主语所到达的最远处。本句的主语是 his knowledge, or recognition, of his surroundings（其中 of his surroundings 作这两个名词的定语），went 是谓语动词。类似表达有：

as far as I know

as far as I am concerned

as far as I can see

as far as 用作连词，接从句。意思由“比较”演变而来：意为“跟......一样远”，还表示情况达到某种程度，意为“远到...；就…而言；在…范围内”（上面的三个表达和网友的句子，都是这个用法）。

The desert continued as far as the eye could see. 沙漠一直伸展到视线的尽头。

They went as far as they could go. 他们尽了最大努力走了那么远的路程。

Professor Swyington Bumper seemed to live in a region all by himself. Though he was on board the Bellaconda, he might just as well have been in an airship, or riding along on the back of a donkey, as far as his knowledge, or recognition, of his surroundings went.

【翻译】斯温顿·邦克教授似乎独自一个人住在一个区域。虽然他是在贝拉康达号船上，但就他对周围环境的了解或认识而言，他好像是（简直就是）坐在飞艇上，或者骑着驴背前行。