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eslint/prefer-const Style

🛠️ An auto-fix is available for this rule for some violations.

What it does

Requires const declarations for variables that are never reassigned after their initial declaration.

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"

"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:

Config (.oxlintrc.json)

{
  "rules": {
    "prefer-const": "error"
  }
}

CLI

oxlint --deny prefer-const

References

• Rule Source