Regex to match words in a sentence by its prefix

Question

I have this regex on mongodb query to match words by prefix:

{sentence: new RegExp(\'^\'+key,\'gi\')}

What would be the right regex pattern

Answer 1

The other answers suggesting the word boundary matching are neat, but will mean that an index isn't used efficiently. If you need fast lookups, you might want to consider adding a field "words" with each of your words broken up, i.e.

{sentence: "This is a dog",
  words: ["This", "is", "a", "dog"]}

After putting an index on the words field, you can go back to using:

{words: new RegExp('^'+key,'gi')}

and a key of "do" will now match this object and use an index.