This line

will push the cursor forward in the sexpr's text. However, due to integer size limitations, the number will no longer be able to increase when the integer cap is hit (in my computer, that number is 1048576), which means the condition if (data.index === data.sexpr.length) return null; is never hit, and therefore the parser gets stuck in an infinite loop for really large inputs.

Solution: I was able to get through this with just a small change

  var data = {
-   index: 0,
+   index: BigInt(0),
    sexpr: sexpr
  }

As far as compatibility goes, according to what I read in https://www.npmjs.com/package/big-integer, BigInt is natively supported in recent versions of Node. I am able to confirm this because I'm using Node 13.5 and didn't have to install anything extra.

I wanted to ask if you think this change is warranted and/or needed, or if I should look into other packages from other languages for my use-case (speed matters).