useDefaultParameterLast

Diagnostic Category: lint/style/useDefaultParameterLast

JavaScript (and super languages)

Since: v1.0.0

Sources:

Same as: default-param-last
Same as: @typescript-eslint/default-param-last

Description

Enforce default function parameters and optional function parameters to be last.

Default and optional parameters that precede a required parameter cannot be omitted at call site.

Examples

Invalid

function f(a = 0, b) {}

code-block.js:1:12 lint/style/useDefaultParameterLast  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ This default parameter should follow the last required parameter or should be a required parameter.
  
  > 1 │ function f(a = 0, b) {}
      │            ^^^^^
    2 │ 
  
  ℹ The last required parameter is here:
  
  > 1 │ function f(a = 0, b) {}
      │                   ^
    2 │ 
  
  ℹ A default parameter that precedes a required parameter cannot be omitted at call site.
  
  ℹ Unsafe fix: Turn the parameter into a required parameter.
  
    1 │ function·f(a·=·0,·b)·{}
      │             ----

function f(a, b = 0, c) {}

code-block.js:1:15 lint/style/useDefaultParameterLast  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ This default parameter should follow the last required parameter or should be a required parameter.
  
  > 1 │ function f(a, b = 0, c) {}
      │               ^^^^^
    2 │ 
  
  ℹ The last required parameter is here:
  
  > 1 │ function f(a, b = 0, c) {}
      │                      ^
    2 │ 
  
  ℹ A default parameter that precedes a required parameter cannot be omitted at call site.
  
  ℹ Unsafe fix: Turn the parameter into a required parameter.
  
    1 │ function·f(a,·b·=·0,·c)·{}
      │                ----

function f(a: number, b?: number, c: number) {}

code-block.ts:1:23 lint/style/useDefaultParameterLast  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ This optional parameter should follow the last required parameter or should be a required parameter.
  
  > 1 │ function f(a: number, b?: number, c: number) {}
      │                       ^^^^^^^^^^
    2 │ 
  
  ℹ The last required parameter is here:
  
  > 1 │ function f(a: number, b?: number, c: number) {}
      │                                   ^^^^^^^^^
    2 │ 
  
  ℹ A optional parameter that precedes a required parameter cannot be omitted at call site.
  
  ℹ Unsafe fix: Turn the parameter into a required parameter.
  
    1 │ function·f(a:·number,·b?:·number,·c:·number)·{}
      │                        -

class Foo {
    constructor(readonly a = 10, readonly b: number) {}
}

code-block.ts:2:17 lint/style/useDefaultParameterLast  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ This default parameter should follow the last required parameter or should be a required parameter.
  
    1 │ class Foo {
  > 2 │     constructor(readonly a = 10, readonly b: number) {}
      │                 ^^^^^^^^^^^^^^^
    3 │ }
    4 │ 
  
  ℹ The last required parameter is here:
  
    1 │ class Foo {
  > 2 │     constructor(readonly a = 10, readonly b: number) {}
      │                                  ^^^^^^^^^^^^^^^^^^
    3 │ }
    4 │ 
  
  ℹ A default parameter that precedes a required parameter cannot be omitted at call site.
  
  ℹ Unsafe fix: Turn the parameter into a required parameter.
  
    2 │ ····constructor(readonly·a·=·10,·readonly·b:·number)·{}
      │                           -----

Valid

function f(a, b = 0) {}

function f(a: number, b?: number, c = 0) {}

function f(a: number, b = 0, c?: number) {}

How to configure

{
  "linter": {
    "rules": {
      "style": {
        "useDefaultParameterLast": "error"
      }
    }
  }
}