From http://www.w3schools.com (Copyright Refsnes Data)

JavaScript RegExp \xxx Character

Definition and Usage

The \xxx character is used to find the Latin character specified by an octal number xxx.

If no match is found, it returns null.

new RegExp("\xxx")

or simply:

/\xxx/

Do a global search for octal number 127 (W) in a string:

var str="Visit W3Schools. Hello World!";
var patt1=/\127/g;

The marked text below shows where the expression gets a match:

Visit W3Schools. Hello World!