Why does set.prototype.difference need to test regex?

[loynoir]

Reproduce

import setDifference1 from "set.prototype.difference"

const sa = new Set([1, 2, 3])
const sb = new Set([3, 4, 5])

console.log(setDifference1(sa, sb))

Expected

$ node reproduce.mjs 
Set(2) { 1, 2 }

Unexpected

$ node --frozen-intrinsics reproduce.mjs 
(node:225431) ExperimentalWarning: The --frozen-intrinsics flag is experimental
(Use `node --trace-warnings ...` to show where the warning was created)
/path/to/node_modules/safe-regex-test/index.js:12
                throw new $TypeError('`regex` must be a RegExp');
                      ^

TypeError <Object <Object <[Object: null prototype] {}>>>: `regex` must be a RegExp
    at regexTester /path/to/node_modules/safe-regex-test/index.js:12:9)
    at Object.<anonymous> /path/to/node_modules/es-abstract/2022/StringToNumber.js:14:16)
    at Module._compile (node:internal/modules/cjs/loader:1254:14)
    at Module._extensions..js (node:internal/modules/cjs/loader:1308:10)
    at Module.load (node:internal/modules/cjs/loader:1117:32)
    at Module._load (node:internal/modules/cjs/loader:958:12)
    at Module.require (node:internal/modules/cjs/loader:1141:19)
    at require (node:internal/modules/cjs/helpers:110:18)
    at Object.<anonymous> /path/to/node_modules/es-abstract/2022/ToNumber.js:10:22)
    at Module._compile (node:internal/modules/cjs/loader:1254:14)

Node.js v18.15.0

Related

inspect-js/is-regex#34

[ljharb]

That’s just an implementation detail (it’s detecting binary/octal/hex prefixes in StringToNumber), but the frozen intrinsics flag isn’t default precisely because it breaks things.

I’ll leave this open for now, but it probably will be closed in favor of inspect-js/is-regex#34

[loynoir]

🤔

But why need StringToNumber?

What are the logical differences compared with https://stackoverflow.com/questions/1723168/what-is-the-fastest-or-most-elegant-way-to-compute-a-set-difference-using-javasc/36504668#36504668

console.clear();

let a = new Set([1, 2, 3, 4]);
let b = new Set([5, 4, 3, 2]);

let a_minus_b = new Set([...a].filter(x => !b.has(x)));
let b_minus_a = new Set([...b].filter(x => !a.has(x)));
let a_intersect_b = new Set([...a].filter(x => b.has(x))); 
let a_union_b = new Set([...a, ...b]); 

console.log(...a_minus_b);     // {1}
console.log(...b_minus_a);     // {5}
console.log(...a_intersect_b); // {2,3,4}
console.log(...a_union_b);     // {1,2,3,4,5}

[ljharb]

Oh, I’m this case it’s not actually invoked by this package, it’s just something that’s evaluated as part of loading the module. That’s what the flag is affecting - you should be able to repro it with nothing except a require of the package.

[ljharb]

(it would be needed if a setlike provided a string size, fwiw)

[ljharb]

I'm going to close this in favor of ljharb/call-bind#4, which is where it would be handled, if at all.

In the meantime, I strongly suggest not using the frozen-intrinsics flag.