Using the immutability setting

We are using the is-immutable-type library to determine the immutability of types. This library can be configure for all rules at once using a shared setting.

Overrides

For details see the overrides section of is-immutable-type.

Resolution order

When looking up an override for a type, the first matching entry wins. User overrides are placed before the built-in defaults, so a user-defined override for a type that also has a default (e.g. Date) takes precedence. Set keepDefault: false to drop the built-in defaults entirely.

Example of configuring immutability overrides

In this example, we are configuring is-immutable-type to treat any readonly array (regardless of the syntax used) as immutable in the case where it was found to be deeply readonly. If it was only found to be shallowly readonly, then no override will be applied.

// .eslintrc.json
{
  // ...
  "settings": {
    "immutability": {
      "overrides": [
        {
          "type": {
            "from": "lib",
            "name": "ReadonlyArray",
          },
          "to": "Immutable",
          "from": "ReadonlyDeep",
        },
      ],
    },
  },
  "rules": {
    // ...
  },
}