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useArrowFunction

Diagnostic Category: lint/complexity/useArrowFunction

Since: v1.0.0

Sources:

Use arrow functions over function expressions.

An arrow function expression is a compact alternative to a regular function expression, with an important distinction: this is not bound to the arrow function. It inherits this from its parent scope.

This rule proposes turning all function expressions that are not generators (function*) and don’t use this into arrow functions.

Examples

Section titled Examples

Invalid

Section titled Invalid
const z = function() {
    return 0;
}
code-block.js:1:11 lint/complexity/useArrowFunction  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ This function expression can be turned into an arrow function.
  
  > 1 │ const z = function() {
      │           ^^^^^^^^^^^^
  > 2 │     return 0;
  > 3 │ }
      │ ^
    4 │ 
  
  ℹ Function expressions that don’t use this can be turned into arrow functions.
  
  ℹ Safe fix: Use an arrow function instead.
  
    1   │ - const·z·=·function()·{
    2   │ - ····return·0;
    3   │ - }
      1 │ + const·z·=·()·=>·0
    4 2 │   
  
const delegatedFetch = async function(url) {
    return await fetch(url);
}
code-block.js:1:24 lint/complexity/useArrowFunction  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ This function expression can be turned into an arrow function.
  
  > 1 │ const delegatedFetch = async function(url) {
      │                        ^^^^^^^^^^^^^^^^^^^^^
  > 2 │     return await fetch(url);
  > 3 │ }
      │ ^
    4 │ 
  
  ℹ Function expressions that don’t use this can be turned into arrow functions.
  
  ℹ Safe fix: Use an arrow function instead.
  
    1   │ - const·delegatedFetch·=·async·function(url)·{
    2   │ - ····return·await·fetch(url);
    3   │ - }
      1 │ + const·delegatedFetch·=·async·(url)·=>·await·fetch(url)
    4 2 │

Valid

Section titled Valid
const f = function() {
    return this.prop;
}

Named function expressions are ignored:

const z = function z() {
    return 0;
}

Function expressions that declare the type of this are also ignored:

const z = function(this: A): number {
    return 0;
}
Section titled Related links