default-param-last

Enforce default parameters to be last.

🧱

This is an "extension" rule that replaces a core ESLint rule to work with TypeScript. See Rules > Extension Rules.

This rule extends the base default-param-last rule from ESLint core. It adds support for optional parameters.

❌ Incorrect

function f(a = 0, b: number) {}
function f(a: number, b = 0, c: number) {}
function f(a: number, b?: number, c: number) {}
class Foo {
  constructor(
    public a = 10,
    private b: number,
  ) {}
}
class Foo {
  constructor(
    public a?: number,
    private b: number,
  ) {}
}

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✅ Correct

function f(a = 0) {}
function f(a: number, b = 0) {}
function f(a: number, b?: number) {}
function f(a: number, b?: number, c = 0) {}
function f(a: number, b = 0, c?: number) {}
class Foo {
  constructor(
    public a,
    private b = 0,
  ) {}
}
class Foo {
  constructor(
    public a,
    private b?: number,
  ) {}
}

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Options

See eslint/default-param-last's options.

How to Use

Flat Config

eslint.config.mjs

export default tseslint.config({
  rules: {
    // Note: you must disable the base rule as it can report incorrect errors
    "default-param-last": "off",
    "@typescript-eslint/default-param-last": "error"
  }
});

Legacy Config

.eslintrc.cjs

module.exports = {
  "rules": {
    // Note: you must disable the base rule as it can report incorrect errors
    "default-param-last": "off",
    "@typescript-eslint/default-param-last": "error"
  }
};

Try this rule in the playground ↗

Resources

• Rule source
• Test source

^{Taken with ❤️ from ESLint core.}