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unicorn/no-immediate-mutation Pedantic

🚧 An auto-fix is planned for this rule, but not implemented at this time.

What it does

Disallows mutating a variable immediately after initialization.

Why is this bad?

When you initialize a variable and immediately mutate it, it's cleaner to include the mutation in the initialization. This makes the code more readable and reduces the number of statements.

Examples

Examples of incorrect code for this rule:

const array = [1, 2];
array.push(3);

const object = { foo: 1 };
object.bar = 2;

const set = new Set([1, 2]);
set.add(3);

const map = new Map([["foo", 1]]);
map.set("bar", 2);

Examples of correct code for this rule:

const array = [1, 2, 3];

const object = { foo: 1, bar: 2 };

const set = new Set([1, 2, 3]);

const map = new Map([
  ["foo", 1],
  ["bar", 2],
]);

How to use

To enable this rule using the config file or in the CLI, you can use:

Config (.oxlintrc.json)

{
  "rules": {
    "unicorn/no-immediate-mutation": "error"
  }
}

Config (oxlint.config.ts)

import { defineConfig } from "oxlint";

export default defineConfig({
  rules: {
    "unicorn/no-immediate-mutation": "error",
  },
});

CLI

oxlint --deny unicorn/no-immediate-mutation

Version

This rule was added in v1.35.0.

References

• Rule Source
• Upstream rule docs
• Open rule in Oxc Playground