Repro

1. Enable the rule (see docs)

2. Either

   • Create a js file where numbers or strings are added

   export const f = (a, b) => a + b;

   • Create a ts file, where arguments of type any are added

   export const f = (a: any, b: any) => a + b;

3. Observe the following error in each case:

   Operands of '+' operation must either be both strings or both numbers.
   eslint(@typescript-eslint/restrict-plus-operands)
   

.eslintrc.js

{
  "rules": {
    "@typescript-eslint/restrict-plus-operands": "error"
  }
}

Expected Result

The current result is fine, however too much strictness out of which you cannot opt out may get the rule challenging to use in existing codebases. I just tried enabling it in a monorepo with mixed js and ts code and got hundreds of errors. I understand the value behind this, just find it impossible to start using the rule to catch real issues (variable of known type number being added to a variable of known type string). Errors in js files are especially unfortunate.

Would it be possible to optionally allow any in the rule?

"@typescript-eslint/restrict-plus-operands":  ["error", { allowAny: true }]

or even

"@typescript-eslint/restrict-plus-operands":  ["error", { skipJs: true }]
"@typescript-eslint/restrict-plus-operands":  ["error", { allowAny: true, skipJs: true }]

Or should js files just be always skipped?

Versions

/cc @armano2 (author of #70)