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+# JavaScript Language Feature Checklist
+So you're working on a new JavaScript feature in SpiderMonkey: Congratulations! Here's a set of checklists and guidelines to help you on your way.
+
+## High Level Feature Ship Checklist.
+(Note: Some of these pieces can happen in parallel, so it's not necessary to
+work directly top-down)
+
+-  ☐ Send an Intent to Prototype email to `dev-platform`.  This is part of the
+  [Exposure Guidelines](https://wiki.mozilla.org/ExposureGuidelines) process. We
+  historically haven't been amazing at sending intent-to-prototype emails, but
+  we can always get better.
+-  ☐ Create a shell option for the feature.
+-  ☐ Stage 2 or earlier proposals should be developed under compile time guards,
+  disabled by default.
+-  ☐ Create a browser preference for the feature.
+-  ☐ Implement the Feature.
+-  ☐ Land feature disabled by pref and shell-option.
+-  ☐ Import the test262 test cases for the feature, or enable them if they're
+  already imported.  (See `js/src/test/Readme.txt` for guidance)
+-  ☐ Contact `fuzzing@mozilla.org` to arrange fuzzing for the feature.
+-  ☐ Add shell option to `js/src/shell/fuzz-flags.txt`. This signals to other
+  fuzzers as well that the feature is ready for fuzzing.
+-  ☐ Send an Intent to Ship Email to `dev-platform`.  This is also part of the
+  [Exposure Guidelines](https://wiki.mozilla.org/ExposureGuidelines) process.
+-  ☐ Ship the feature; default the preference to true and the command-line
+  option to true.
+-  ☐ Open a followup bug to later remove the preference and the command line
+  option.
+
+
+## Supplemental Checklists
+### Shipping Consideration Checklist
+
+-  ☐ If it seems possible that the feature will cause webcompat issues,
+  consider shipping `NIGHTLY_ONLY` for a cycle or two, to use nightly as an
+  attempt to shake out potential webcompat issues.
+
+
+### Web Platform Integration Checklist
+
+_Sometimes Complexity of the web-platform leaks into JS Feature works_
+
+-  ☐ Ensure the appropriate web-platform tests exist, and are being run.
+-  ☐ Is your feature correctly enabled inside of Workers? (They have different
+  option set than main thread, and it's easy to forget them!) You may want to
+  write a mochitest.
+
+### Syntax Features Checklist
+
+-  ☐ Does `Reflect.parse` correctly parse and return results for your new syntax?
+  - `Reflect.parse` tests are interesting as well, because they can be written
+    for new syntax before bytecode emission is done.
+  -  ☐ Are the locations correct for the new syntax entries in the parse tree?
+-  ☐ Are your errors emitted with sensible location info?
+
+### Testing Consideration Checklist
+
+_There's lots of complexity in SpiderMonkey that isn't always captured by the
+specification, so the below is some useful guidance to behaviour to pay
+attention to that may not be tested by a feature's test262 tests_
+
+-  ☐ How does your feature interact with multiple compartments? What happens if
+  references happen across compartments, or if `this` is a
+  `CrossCompartmentWrapper`?
+-  ☐ Are your error messages being emitted in the correct realm, with the
+  correct prototype?
+-  ☐ If async functions or promises are involved, are user-code objects
+  resolved? If so, does the feature correctly handle [the `.then` property
+  behaviour of promise
+  resolution?](https://www.stefanjudis.com/today-i-learned/promise-resolution-with-objects-including-a-then-property/)
+-  ☐ Have you written some OOM tests for your feature to ensure your OOM
+  handling is correct?
+
+#### Web Platform Testing Considerations
+-  ☐ Does the feature have to handle exotic objects specially? Consider what
+  happens when your feature interacts with the very exotic objects on the web
+  platform, such as `WindowProxy`, `Location` (cross-origin objects).
+-  ☐ What happens when your feature interacts with
+  [X-rays](/dom/scriptSecurity/xray_vision.rst)?