technically, you're talking about writing a lexical analyzer that matches the longest possible string, not a parser.
as for loading the dictionary, I don't think it would be that difficult. A linked list probably would not be a good approach, because the dictionary probably would not be changing very much at run-time. An static array of sorted arrays would probably be a reasonable approach. I would definitely say put the declaration in a separate js file. You could also put a function declaration in that file that performed something like a binary search through each of the word groups. There might be a better way to do it than that, but it would probably be pretty complicated.