Doesn't Flag LookBehind Regexp on Firefox 77

https://kangax.github.io/compat-table/es2016plus/ shows Firefox 77 isn’t compatible with the regexp lookbehind feature, firefox 78 release notes show it added it in that release (same table shows and confirms the same)

npx browserslist shows firefox 77 is in the defaults, which we use. why wasn’t this caught? we had a look behind that passed the linter, and caused our app to fail on Firefox 77.

eslintrc config:

env:
  browser: true
  es6: true
extends:
  - standard
  - plugin:compat/recommended
globals:
  Atomics: readonly
  SharedArrayBuffer: readonly
parser: babel-eslint
parserOptions:
  ecmaFeatures:
    jsx: true
    experimentalObjectRestSpread: true
  ecmaVersion: 2018
  sourceType: module
plugins:
  - react
  - unused-imports
  - compat
  - es
rules: {
  "react/jsx-uses-react" : "error", 
 # "max-len" : ['error',{ code: 120,ignorePattern: 'import.*| .*:.*' }], #these ignore import statements as well as the agent.js file example where we have a dictionary of constants that can be long.
  "react/jsx-uses-vars": "error",
  "compat/compat": "error",
  "no-console": 1,
  "unused-imports/no-unused-imports": 2,
  "unused-imports/no-unused-vars": 1,
  "lines-between-class-members": 2,
  "padding-line-between-statements": ['error',{ blankLine: "always", prev: "function", next: "function" },{ blankLine: "always", prev: "multiline-const", next: "multiline-const" }],
  "import/newline-after-import": ["error"]
}

[curiousdannii]

Look behinds are unsupported in Safari but this plugin didn’t show the problem. I don’t use Babel, and @babel/eslint-parser doesn’t appear to do browser checking like this plugin does.

It’s fine for this project to set its scope firmly (though I wish that was explained a little more clearly in the readme). Anyone know of any other packages that can test ES syntax features?

[ljharb]

That’s what babel and babel-eslint is for.