gistfile1.md

RegExp.escape(string)

Computes a new version of a String value in which certain characters have been escaped, so that the regular expression engine will interpret any metacharacters that it may contain as character literals.

When the escape function is called with one argument string, the following steps are taken:

1. Let string be ToString(string).
2. ReturnIfAbrupt(string).
3. Let length be the number of characters in string.
4. Let R be the empty string.
5. Let k be 0.
6. Repeat, while k < length, 1. Let C be the character at position k within string. 1. If C is one of the 16 nonblank characters "-[]{}()*+?.,\^$|" then,
   1. Let S be a String containing two characters "\x" where x is a C character. 1. Else,
   2. Let S be a String containing the single C character. 1. Let R be a new String value computed by concatenating the previous value of R and S. 1. Increase k by 1.
7. Return R.

https://github.com/benjamingr/RexExp.escape/blob/master/README.md#regexpescapes

There's also a precendent in the EscapeRegExpPattern production, which is careful to specify the results without constraining the exact implementation too closely. On the other hand, specifying an exact result might be better...