prefer-spread.md

Expected Behavior: prefer-spread Rule

This rule enforces the use of spread syntax (...) over manual array operations like Array.from() and array.concat().

Examples

Array.from() Conversion

- const array1 = Array.from(iterable)
+ const array1 = [...iterable]

- const array2 = Array.from(nodeList)
+ const array2 = [...nodeList]

- const array3 = Array.from(set)
+ const array3 = [...set]

Array.concat() Replacement

- const combined1 = arr.concat(otherArr)
+ const combined1 = [...arr, ...otherArr]

- const combined2 = arr.concat(item1, item2)
+ const combined2 = [...arr, item1, item2]

- const combined3 = arr.concat(arr1, arr2, arr3)
+ const combined3 = [...arr, ...arr1, ...arr2, ...arr3]

Function Returns

  function processData(data) {
-   return Array.from(data)
+   return [...data]
  }

  function combineArrays() {
-   return arr.concat(otherArr)
+   return [...arr, ...otherArr]
  }

Object Properties

  const config = {
-   items: Array.from(iterable)
+   items: [...iterable]
  }

- const results = [Array.from(data), Array.from(otherData)]
+ const results = [[...data], [...otherData]]

Class Methods

  class DataProcessor {
    combine(data) {
-     return this.items.concat(data)
+     return [...this.items, ...data]
    }
  }

Rule Scope

This rule only applies to:

• ✅ Array.from() with a single argument
• ✅ array.concat() with one or more arguments

This rule does NOT apply to:

• ❌ Array.from() with multiple arguments (mapping function)
• ❌ array.concat() with no arguments
• ❌ Already using spread syntax
• ❌ Other array methods (filter, map, reduce, etc.)

Covered Operations

This rule applies to the following operations:

• ✅ Array.from(iterable) → [...iterable]
• ✅ arr.concat(otherArr) → [...arr, ...otherArr]
• ✅ arr.concat(item1, item2) → [...arr, item1, item2]
• ✅ arr.concat(arr1, arr2) → [...arr, ...arr1, ...arr2]

Auto-fix Behavior

The rule provides auto-fix suggestions that convert manual array operations to spread syntax:

• Array.from(iterable) → [...iterable]
• arr.concat(otherArr) → [...arr, ...otherArr]
• arr.concat(item1, item2) → [...arr, item1, item2]
• arr.concat(arr1, arr2) → [...arr, ...arr1, ...arr2]