prefer-ts-extras-is-integer

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

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

Targeted pattern scope

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

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

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

What this rule reports

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

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

Why this rule exists

isInteger standardizes whole-number validation with the rest of the ts-extras numeric predicate family.

Numeric guard naming is consistent.
Native/helper predicate mixing is reduced.
Integer validation reads the same across services and packages.

❌ Incorrect

const isWhole = Number.isInteger(value);

✅ Correct

const isWhole = isInteger(value);

Behavior and migration notes

Runtime behavior matches native Number.isInteger.
Decimal numbers still return false.
Numeric strings are not coerced to numbers.

Additional examples

❌ Incorrect — Additional example

if (Number.isInteger(retryCount)) {
    useRetries(retryCount);
}

✅ Correct — Additional example

if (isInteger(retryCount)) {
    useRetries(retryCount);
}

✅ Correct — Repository-wide usage

const whole = isInteger(userInput);

ESLint flat config example

import typefest from "eslint-plugin-typefest";

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

When not to use it

Disable this rule if your codebase requires direct Number.isInteger usage.

Package documentation

ts-extras package documentation:

Source file: source/is-integer.ts

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

@category Improved builtin
@category Type guard
*/

Rule catalog ID: R020

prefer-ts-extras-is-integer

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