Question

I was looking for a trim function in JavaScript which doesn’t exist and some code on Googling suggests that use:

function trimStr(str) {
  return str.replace(/^\s+|\s+$/g, '');
}

I want to know how str.replace(/^\s+|\s+$/g, '')
works. I understand that this is some form of regular expression but dont know what it is doing.

Answer 1

/^\s+|\s+$/g searches for whitespace from either the beginning or the end of the string. The expression can be split into two parts, ^\s+ and \s+$ which are separated by | (OR). The first part starts from the beginning of the string (^) and includes as many whitespace characters it can (\s+). The second part does the same but in reverse and for the end using the dollar sign ($).

In plain english, the regular expression would go like this:

Find as many whitespace characters from the beginning of the string as possible or as many whitespace characters from the end as possible.

Note that \s matches spaces, tabs and line breaks.

The /g part at the end enables global searching, which allows multiple replacements (eg. not just the beginning, but the end of the string also).