prefer-type-fest-json-array

Require TypeFest JsonArray over explicit JsonValue array-union aliases.

Targeted pattern scope

This rule matches explicit JSON array alias spellings where JsonArray communicates intent directly.

JsonValue[] | readonly JsonValue[]
Array<JsonValue> | ReadonlyArray<JsonValue>

This rule intentionally excludes other array aliases and non-JSON payload array forms.

What this rule reports

This rule reports explicit JsonValue array alias forms that should use JsonArray.

JsonValue[] | readonly JsonValue[]
Array<JsonValue> | ReadonlyArray<JsonValue>

Why this rule exists

JsonArray communicates JSON array intent directly and avoids repeating equivalent array union shapes.

❌ Incorrect

type Payload = JsonValue[] | readonly JsonValue[];

✅ Correct

type Payload = JsonArray;

Behavior and migration notes

JsonArray is the canonical alias for JSON arrays in type-fest.
Keep JsonValue[] | readonly JsonValue[] usage out of shared contracts to avoid duplicate representations.
Prefer one canonical alias per concept to reduce type alias drift across packages.

Additional examples

❌ Incorrect — Additional example

type Payload = Array<JsonValue>;

✅ Correct — Additional example

type Payload = JsonArray;

✅ Correct — Repository-wide usage

type SerializedRows = JsonArray;

ESLint flat config example

import typefest from "eslint-plugin-typefest";

export default [
    {
        plugins: { typefest },
        rules: {
            "typefest/prefer-type-fest-json-array": "error",
        },
    },
];

When not to use it

Disable this rule if public APIs must preserve existing custom alias names for compatibility.

Package documentation

TypeFest package documentation:

Source file: source/json-value.d.ts

/**
Matches a JSON array.

@category JSON
*/

Rule catalog ID: R043

prefer-type-fest-json-array

Targeted pattern scope

What this rule reports

Why this rule exists

❌ Incorrect

✅ Correct

Behavior and migration notes

Additional examples

❌ Incorrect — Additional example

✅ Correct — Additional example

✅ Correct — Repository-wide usage

ESLint flat config example

When not to use it

Package documentation

Further reading

Adoption resources

Targeted pattern scope​

What this rule reports​

Why this rule exists​

❌ Incorrect​

✅ Correct​

Behavior and migration notes​

Additional examples​

❌ Incorrect — Additional example​

✅ Correct — Additional example​

✅ Correct — Repository-wide usage​

ESLint flat config example​

When not to use it​

Package documentation​

Further reading​

Adoption resources​

Targeted pattern scope

What this rule reports

Why this rule exists

❌ Incorrect

✅ Correct

Behavior and migration notes

Additional examples

❌ Incorrect — Additional example

✅ Correct — Additional example

✅ Correct — Repository-wide usage

ESLint flat config example

When not to use it

Package documentation

Further reading

Adoption resources