prefer-ts-extras-is-finite

Prefer isFinite from ts-extras over Number.isFinite(...).

This keeps predicate usage consistent with other ts-extras narrowing helpers.

Targeted pattern scope

This rule focuses on direct Number.isFinite(value) calls that can be migrated to isFinite(value) with deterministic fixes.

Number.isFinite(value) call sites that can use isFinite(value).

Alias indirection, wrapper helpers, and non-canonical call shapes are excluded to keep isFinite(value) migrations safe.

What this rule reports

This rule reports Number.isFinite(value) call sites when isFinite(value) is the intended replacement.

Number.isFinite(value) call sites that can use isFinite(value).

Why this rule exists

isFinite keeps numeric predicate usage aligned with the rest of the ts-extras guard set.

Numeric validation helpers use one naming/style convention.
Native/helper mixing in guard-heavy code is reduced.
Number guard logic stays consistent across modules.

❌ Incorrect

const isValid = Number.isFinite(value);

✅ Correct

const isValid = isFinite(value);

Behavior and migration notes

Runtime behavior matches native Number.isFinite.
Only numbers are considered; numeric strings are not coerced.
NaN, Infinity, and -Infinity still return false.

Additional examples

❌ Incorrect — Additional example

if (Number.isFinite(metric)) {
    consume(metric);
}

✅ Correct — Additional example

if (isFinite(metric)) {
    consume(metric);
}

✅ Correct — Repository-wide usage

const valid = isFinite(durationMs);

ESLint flat config example

import typefest from "eslint-plugin-typefest";

export default [
    {
        plugins: { typefest },
        rules: {
            "typefest/prefer-ts-extras-is-finite": "error",
        },
    },
];

When not to use it

Disable this rule if your team explicitly standardizes on native Number.isFinite calls.

Package documentation

ts-extras package documentation:

Source file: source/is-finite.ts

/**
A strongly-typed version of `Number.isFinite()`.

@category Improved builtin
@category Type guard
*/

Rule catalog ID: R018

prefer-ts-extras-is-finite

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