Regular expression to remove spaces at the beginning/end of words?

Question

JavaScript

How to compose a regular expression so that spaces are removed at the beginning of the line before the word (_word), at the end of the line after the word (word_) and replace double or more spaces between two words (word_word) with a single one.
Detailed example:
Source string (_word1_word2__word3_)
String that is needed as a result (word1_word2_word3)

Answer 1

You do not need regular expressions for this, there is an excellent trim function

Answer 2

/(\s{2,}/
replace with one space