defaultParameterLast

Enforce default parameters to be last.

✅ This rule is included in the ts untyped presets.

Putting default parameters last allows function calls to omit optional tail arguments. When default parameters appear before required ones, callers must explicitly pass undefined to skip them.

This rule reports parameters with default values or optional markers (?) that appear before required parameters.

function 
function greet(name: string | undefined, greeting: string): void
greet(
name: string
name = "World", 
greeting: string
greeting: string) {
  
var console: Console
The console module provides a simple debugging console that is similar to the
JavaScript console mechanism provided by web browsers.
The module exports two specific components:

A Console class with methods such as console.log(), console.error() and console.warn() that can be used to write to any Node.js stream.
A global console instance configured to write to process.stdout and
process.stderr. The global console can be used without importing the node:console module.

Warning: The global console object's methods are neither consistently
synchronous like the browser APIs they resemble, nor are they consistently
asynchronous like all other Node.js streams. See the note on process I/O for
more information.
Example using the global console:
console.log('hello world');
// Prints: hello world, to stdout
console.log('hello %s', 'world');
// Prints: hello world, to stdout
console.error(new Error('Whoops, something bad happened'));
// Prints error message and stack trace to stderr:
//   Error: Whoops, something bad happened
//     at [eval]:5:15
//     at Script.runInThisContext (node:vm:132:18)
//     at Object.runInThisContext (node:vm:309:38)
//     at node:internal/process/execution:77:19
//     at [eval]-wrapper:6:22
//     at evalScript (node:internal/process/execution:76:60)
//     at node:internal/main/eval_string:23:3

const name = 'Will Robinson';
console.warn(`Danger ${name}! Danger!`);
// Prints: Danger Will Robinson! Danger!, to stderr
Example using the Console class:
const out = getStreamSomehow();
const err = getStreamSomehow();
const myConsole = new console.Console(out, err);

myConsole.log('hello world');
// Prints: hello world, to out
myConsole.log('hello %s', 'world');
// Prints: hello world, to out
myConsole.error(new Error('Whoops, something bad happened'));
// Prints: [Error: Whoops, something bad happened], to err

const name = 'Will Robinson';
myConsole.warn(`Danger ${name}! Danger!`);
// Prints: Danger Will Robinson! Danger!, to err
@see ― source
console.
Console.log(message?: any, ...optionalParams: any[]): void (+1 overload)
Prints to stdout with newline. Multiple arguments can be passed, with the
first used as the primary message and all additional used as substitution
values similar to printf(3)
(the arguments are all passed to util.format()).
const count = 5;
console.log('count: %d', count);
// Prints: count: 5, to stdout
console.log('count:', count);
// Prints: count: 5, to stdout
See util.format() for more information.
@since ― v0.1.100
log(`${
greeting: string
greeting}, ${
name: string
name}!`);
}

function 
function calculate(a: number | undefined, b: number, c?: number): number
calculate(
a: number
a = 1, 
b: number
b: number, 
c: number
c = 2) {
  return 
a: number
a + 
b: number
b + 
c: number
c;
}

const 
const fn: (x: number | undefined, y: number) => number
fn = (
x: number
x = 0, 
y: number
y: number) => 
x: number
x + 
y: number
y;

function 
function example(a?: number, b: number): number
example(
a: number | undefined
a?: number, 
b: number
b: number) {
  return (
a: number | undefined
a ?? 0) + 
b: number
b;
}

function 
function greet(greeting: string, name?: string): void
greet(
greeting: string
greeting: string, 
name: string
name = "World") {
  
var console: Console
The console module provides a simple debugging console that is similar to the
JavaScript console mechanism provided by web browsers.
The module exports two specific components:

A Console class with methods such as console.log(), console.error() and console.warn() that can be used to write to any Node.js stream.
A global console instance configured to write to process.stdout and
process.stderr. The global console can be used without importing the node:console module.

Warning: The global console object's methods are neither consistently
synchronous like the browser APIs they resemble, nor are they consistently
asynchronous like all other Node.js streams. See the note on process I/O for
more information.
Example using the global console:
console.log('hello world');
// Prints: hello world, to stdout
console.log('hello %s', 'world');
// Prints: hello world, to stdout
console.error(new Error('Whoops, something bad happened'));
// Prints error message and stack trace to stderr:
//   Error: Whoops, something bad happened
//     at [eval]:5:15
//     at Script.runInThisContext (node:vm:132:18)
//     at Object.runInThisContext (node:vm:309:38)
//     at node:internal/process/execution:77:19
//     at [eval]-wrapper:6:22
//     at evalScript (node:internal/process/execution:76:60)
//     at node:internal/main/eval_string:23:3

const name = 'Will Robinson';
console.warn(`Danger ${name}! Danger!`);
// Prints: Danger Will Robinson! Danger!, to stderr
Example using the Console class:
const out = getStreamSomehow();
const err = getStreamSomehow();
const myConsole = new console.Console(out, err);

myConsole.log('hello world');
// Prints: hello world, to out
myConsole.log('hello %s', 'world');
// Prints: hello world, to out
myConsole.error(new Error('Whoops, something bad happened'));
// Prints: [Error: Whoops, something bad happened], to err

const name = 'Will Robinson';
myConsole.warn(`Danger ${name}! Danger!`);
// Prints: Danger Will Robinson! Danger!, to err
@see ― source
console.
Console.log(message?: any, ...optionalParams: any[]): void (+1 overload)
Prints to stdout with newline. Multiple arguments can be passed, with the
first used as the primary message and all additional used as substitution
values similar to printf(3)
(the arguments are all passed to util.format()).
const count = 5;
console.log('count: %d', count);
// Prints: count: 5, to stdout
console.log('count:', count);
// Prints: count: 5, to stdout
See util.format() for more information.
@since ― v0.1.100
log(`${
greeting: string
greeting}, ${
name: string
name}!`);
}

function 
function calculate(b: number, a?: number, c?: number): number
calculate(
b: number
b: number, 
a: number
a = 1, 
c: number
c = 2) {
  return 
a: number
a + 
b: number
b + 
c: number
c;
}

const 
const fn: (y: number, x?: number) => number
fn = (
y: number
y: number, 
x: number
x = 0) => 
x: number
x + 
y: number
y;

function 
function example(a?: number, ...rest: number[]): number
example(
a: number
a = 1, ...
rest: number[]
rest: number[]) {
  return 
rest: number[]
rest.
Array<number>.reduce(callbackfn: (previousValue: number, currentValue: number, currentIndex: number, array: number[]) => number, initialValue: number): number (+2 overloads)
Calls the specified callback function for all the elements in an array. The return value of the callback function is the accumulated result, and is provided as an argument in the next call to the callback function.
@param ― callbackfn A function that accepts up to four arguments. The reduce method calls the callbackfn function one time for each element in the array.
@param ― initialValue If initialValue is specified, it is used as the initial value to start the accumulation. The first call to the callbackfn function provides this value as an argument instead of an array value.
reduce((
sum: number
sum, 
value: number
value) => 
sum: number
sum + 
value: number
value, 
a: number
a);
}

Options

This rule is not configurable.

When Not To Use It

If your API design intentionally places default parameters before required ones for readability or documentation purposes, you may disable this rule. Some legacy APIs may also have established parameter orderings that cannot be changed without breaking changes.

Equivalents in Other Linters

Biome: useDefaultParameterLast
Deno: default-param-last
ESLint: default-param-last@typescript-eslint/default-param-last
Oxlint: eslint/default-param-last

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defaultParameterLast

Examples

Options

When Not To Use It

Further Reading

Equivalents in Other Linters