@typescript-eslint/default-param-last

A default value only applies when the argument is left out or is undefined. If a required parameter follows, the caller can't leave the first one out and has to pass undefined to get the default.

Optional parameters (label?: string) are treated like parameters with a default.

It's the TypeScript version of default-param-last and reports the same code.

With bunfig.toml you can set either name. bun lint runs this rule in TypeScript files and default-param-last in JavaScript files, so nothing is reported twice. With an ESLint config, turn on only one of the two.

Configure

Off by default. To turn it on:

[lint.rules]
"@typescript-eslint/default-param-last" = "error" # or "warn"

Examples

Reported:

function connect(port = 3000, host: string) {}

connect(undefined, "localhost");

function connect(port?: number, host: string) {}

class Client {
  constructor(private retries = 3, private url: string) {}
}

Not reported:

function connect(host: string, port = 3000) {}

connect("localhost");

function request(url: string, retries = 3, label?: string, ...headers: string[]) {}