Getting `ReferenceError: dis is not defined` when using Spidermonkey's JS shell

Question

According to the Spidermonkey hacking tips documentation, the JS Shell provides a function called dis that dumps the bytecode of a function. However, when I try to use it, I get an error:

Code:

function main() {
  console.log('Hello World');
}

dis(main);

Error: ReferenceError: dis is not defined

Setup Details:

• JS Shell downloaded from Mozilla nightly archive
• Platform: Linux (x86_64)
• JS Shell version: JavaScript-C137.0a1