How does this JavaScript RegExp work?

Question

I am lost about how this works:

x=x.replace(/^\s+|\s+$/g,"");

What is the pipe( | ) for ?

Answer 1

The pipe means "or".

So your regex matches

^    # the start of the string
/s+  # followed by whitespace (one or more characters)
|    # or
/s+  # whitespace
$    # followed by the end of the string

The /g (global) modifier applies the regex to all matches in the string, not just the first one.

Answer 2

It means or. The part to the left matches any leading spaces (^), the part to the right matches any trailing space ($). The g modifier allows this matching to be applied more than once, which is useful if you're expecting both trailing and leading space.

Basically this regex trims whitespace.

An alternative way to write this regex is, using the new RegExp construct:

x = x.replace(new RegExp("^\s+|\s+$", "g"), "");

If find this notation more readable because you don't need your delimiters (/) and your modifier is separated.