eslint/prefer-const Style
What it does
Requires const declarations for variables that are never reassigned after their initial declaration.
Ignored Files
This rule ignores .svelte and .vue files entirely. Oxlint only parses the <script> blocks of these files, so a binding that the template reassigns looks like it is never reassigned, and turning it into a const makes the framework compiler fail. In Svelte the template writes through bind:this={el} and bind:value={x}; in Vue a <script setup> let is a setup-let binding that v-model="x" and inline handlers such as @click="x = 1" assign to directly.
Why is this bad?
If a variable is never reassigned, using the const declaration is better. const declaration tells readers, "this variable is never reassigned," reducing cognitive load and improving maintainability.
Examples
Examples of incorrect code for this rule:
let a = 3;
console.log(a);
let b;
b = 0;
console.log(b);
for (let i in [1, 2, 3]) {
console.log(i);
}Examples of correct code for this rule:
const a = 0;
let a;
a = 0;
a = 1;
let a;
if (true) {
a = 0;
}
for (const i in [1, 2, 3]) {
console.log(i);
}Configuration
destructuring
type: "any" | "all"
Configures how destructuring assignments are handled.
"any"
Warn if any of the variables in a destructuring assignment should be const.
"all"
Only warn if all variables in a destructuring assignment should be const. Otherwise, ignore them.
ignoreReadBeforeAssign
type: boolean
default: false
If true, the rule will not report variables that are read before their initial assignment. This is mainly useful for preventing conflicts with the typescript/no-use-before-define rule.
How to use
To enable this rule using the config file or in the CLI, you can use:
{
"rules": {
"prefer-const": "error"
}
}import { defineConfig } from "oxlint";
export default defineConfig({
rules: {
"prefer-const": "error",
},
});oxlint --deny prefer-constVersion
This rule was added in v1.43.0.