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

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

What would be the right regex pattern if I want it to match a sentence that has at least a word starting with key prefix? For example:

If I have a sentence

This is a dog

when key is 'do', then it should match that sentence since prefix 'do' is a substring of 'dog'.

My solution as of now only works for the first word of the sentence. It so far only matches that sentence if I type in 't' or 'th' or 'this'. It wouldnt match that sentence whenever I type in 'i' (prefix for 'is') or 'do' (prefix for 'dog').