Oh One Brow.....
Alas, you are both wrong, and so is the dictionary in this case. The very fact that we can and do separate the word from the rest of the sentence with a comma, as well as that it's used to change the tone of a sentence, not a word, means that alas is neither adverb nor "connector" (conjunction?), but is an interjection.
My posts are all tongue-in-cheek and I conceded to candrew's point with my "touche" and my facetious counterargument. So first, I tip my hat to candrew, for his accurate correction of my earlier post and his respectful and cogent arguments.
One Brow, on the other hand (perhaps in jest?) has gone off the deep end by claiming that alas is neither adverb nor conjunction, because it can be separated with a comma.
You can find similar explanations all over the web from reputable sources, here is one that sums it up nicely:
"Sentence connectors join whole statements in clause or sentence form. Because some of these relationship words have adverbial forms (obviously, naturally, unfortunately), they are sometimes called conjunctive adverbs. The most common sentence connectors are therefore, however, consequently, thus, then, in fact, moreover, nevertheless, so, in addition, meanwhile."
https://www.zaneeducation.com/education/literary-arts/sentence-connectors-and-interjection.php
Also,
https://www.writingcentre.uottawa.ca/hypergrammar/adverbs.html
Moreover, the notion that an adverb can only change the tone of a word and not the tone of a sentence is pure comedy.
Wikipedia gets this one right: "An adverb is a word that changes or qualifies the meaning of a verb, adjective, other adverb, clause, sentence or any other word or phrase...."