So my boss is being a dick and often updates the feature spec

>>18681948
>updates the feature spec just before I am finished implementing the first specification.

>As a result he thinks I am slow

ARE you slow? Maybe it's because you don't get the job done that he has the opportunity and time to re-think it.

Just send your resignation and post a bad review on glassdoor.

>>18681948
>webdev

My understanding is that being a webdev involves eating shit from clients. Another way to put it is you're in the shit eating business.

Just being entirely honest as someone who built a complex magento store with zero knowledge and has experienced these headaches you speak of after being quoted in the region of 4-10k from local companies/webdevs to do it and thinking fuck it, I can do just as good a job. If I paid top dollar to have someone do it for me I would be expecting you to eat all my nutty changes at my every whim, no matter how stupid, and thank me for the priv. Be grateful you aren't dealing with clients, the clients changes might have been a lot crazier if it wasn't for whoever spent 4 hours on the phone with them 'managing their expectations'.

Just be sure to ask your manager to email you every time he updates the spec sheet, and take frequent captures of it.

Also start looking for another job... You might find it's like this everywhere if this is your first job in this particular field. Even a bit of freelancing will let you know how demanding customers are.