[jbboehr]

> FWIW JS does not have a similar capability so I can't add a note there

This example on MDN seems to indicate that you can, am I misunderstanding it?

  const bigJSON = '{"gross_gdp": 12345678901234567890}';
  const bigObj = JSON.parse(bigJSON, (key, value, context) => {
    if (key === "gross_gdp") {
      // Ignore the value because it has already lost precision
      return BigInt(context.source);
    }
    return value;
  });

[0]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Refe...

[js2]

> am I misunderstanding it?

The optional `context` parameter is a tc39 proposal. The feature compatibility matrix on the bottom of the MDN page is really confusing because it's showing only when `JSON.parse` was added, not whether the optional `context` parameter is supported.

I've confirmed it's available in:

  - V8 11.4.31
  - Node 20.12.0 (with `--harmony`)
  - Node 21.7.1 (without requiring `--harmony`)
  - Chrome 123.0.6312.107

But not available in:

  Firefox 124.0.2 (ironically) 
  Safari 17.3.1

The original blog post linked to the proposal:

https://tc39.es/proposal-json-parse-with-source/

https://github.com/tc39/proposal-json-parse-with-source

This issue links to the various browser engine tracking bugs:

https://github.com/tc39/proposal-json-parse-with-source/issu...

Which are:

• Chrome/V8: https://bugs.chromium.org/p/v8/issues/detail?id=12955

• Firefox/SpiderMonkey: https://bugzilla.mozilla.org/show_bug.cgi?id=1658310

• Safari/JavaScriptCore: https://bugs.webkit.org/show_bug.cgi?id=248031

[js2]

The MDN PR documenting the optional `context` parameter was merged just 2 weeks ago:

https://github.com/mdn/content/pull/32697/files