prefer-const

Suggest const for variables that are initialized and never reassigned.

• Rule ID: prefer-const (also accepted as pickier/prefer-const in config)
• Severity: configurable via pluginRules
• Options: none

Description

When a variable is declared with let or var, initialized on the same line, and never reassigned, this rule suggests using const instead. Destructuring declarations are skipped to avoid false positives.

This is a heuristic rule implemented in the built-in plugin. It scans lines for simple declarations and then looks for reassignments or ++/-- usage later in the file.

Examples

Code that triggers the rule:

const count = 1
function inc() {
  console.log(count)
}

Suggested change:

const count = 1
function inc() {
  console.log(count)
}

Code that does not trigger the rule:

let total = 0
for (const n of [1, 2, 3])
  total += n // reassigned

Configuration

Enable the rule via pluginRules in your pickier config:

// pickier.config.ts
export default {
  pluginRules: {
    'prefer-const': 'error',
    // or: 'pickier/prefer-const': 'error'
  },
}

This rule is implemented in the built-in plugin inside the linter, alongside other sorting and style checks.