sucrase/dist/src/transformers/NumericSeparatorTransformer.mjs

Super-fast alternative to Babel for when you can target modern JS runtimes

import Transformer from "./Transformer";
export default class NumericSeparatorTransformer extends Transformer {
    constructor(tokens) {
        super();
        this.tokens = tokens;
    }
    process() {
        if (this.tokens.matches(["num"])) {
            const code = this.tokens.currentTokenCode();
            if (code.includes("_")) {
                this.tokens.replaceToken(code.replace(/_/g, ""));
                return true;
            }
        }
        return false;
    }
}