What does RegExp.$1 do

Question

I have come across a piece of code in JScript:

RegExp.$1

Does anybody know what it does?

If I output it on its own, I get nothing not e

Answer 1

These work in conjunction with capturing parentheses. For example, /(foo)/ matches and remembers 'foo' in "foo bar." The matched substring can be recalled from the resulting array's elements [1], ..., [n] or from the predefined RegExp object's properties $1, ..., $9.

In your example, the $1 refers to the match made by (.+)

See https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp