radix

Without a radix, parseInt picks the base from the string, so parseInt("0x10") is 16, while parseInt("0x10", 10) is 0. With input from a user or a file, that's rarely what you want. The second argument says which base you mean.

The rule checks parseInt and Number.parseInt. It also reports a call without arguments, and a radix that can't work: undefined, or a literal that isn't a whole number from 2 to 36.

For a missing radix, the report comes with a suggestion that adds 10.

Configure

Off by default. To turn it on:

[lint.rules]
"radix" = "error" # or "warn"

Every option, set to its default:

[lint.rules]
"radix" = ["error", "always"] # "always" or "as-needed"

Examples

Reported:

const page = parseInt(query.page);
const size = Number.parseInt(query.size);
const level = parseInt(input, 1);
const depth = parseInt(input, "10");

Not reported:

const page = parseInt(query.page, 10);
const color = Number.parseInt(hex, 16);
const value = parseInt(input, base);

Options

Option	What it does
"always" (default)	Require the radix.
"as-needed"	Has no effect, as in ESLint 10.

const page = parseInt(query.page);

If your project has an ESLint config and ESLint 9 or older installed, "as-needed" works like it does there. You can leave the radix out, and a radix of 10 is reported.