prefer-const.md

pageClass	sidebarDepth	title	description
rule-details	0	svelte/prefer-const	Require `const` declarations for variables that are never reassigned after declared

svelte/prefer-const

Require const declarations for variables that are never reassigned after declared

• ❗ This rule has not been released yet.
• 🔧 The --fix option on the command line can automatically fix some of the problems reported by this rule.

📖 Rule Details

This rule reports the same as the base ESLint prefer-const rule, except that ignores Svelte reactive values such as $state, $derived and $props. If this rule is active, make sure to disable the base prefer-const rule, as it will conflict with this rule.

<script>
  /* eslint svelte/prefer-const: "error" */

  // ✓ GOOD
  const { a, b } = $props();
  let { a, b } = $state();

  // ✗ BAD
  // Imagine obj is not re-assigned, therefore it should be constant
  let obj = { a, b };
</script>

🔧 Options

{
  "svelte/prefer-const": [
    "error",
    {
      "destructuring": "any",
      "ignoreReadonly": true
    }
  ]
}

• destructuring: The kind of the way to address variables in destructuring. There are 2 values:
  • any (default): if any variables in destructuring should be const, this rule warns for those variables.
  • all: if all variables in destructuring should be const, this rule warns the variables. Otherwise, ignores them.
• ignoreReadonly: If true, this rule will ignore variables that are read between the declaration and the first assignment.

📚 Further Reading

• See ESLint prefer-const rule for more information about the base rule.

🔍 Implementation

• Rule source
• Test source

^{Taken with ❤️ from ESLint core}