prefer-readonly

Require readonly for private fields never mutated after initialization

A private field that is never mutated after initialization grants unnecessary write access inside its declaration.
Instead, you SHOULD mark the field readonly so later mutation is rejected.

- Category: style
- Level: warning
- Fix: automatic
- Scope: module

Reported

class User {
    private name: string;

    constructor(name: string) {
        this.name = name;
    }

    describe(): string {
        return this.name;
    }
}
Accepted

class User {
    private readonly name: string;

    constructor(name: string) {
        this.name = name;
    }

    describe(): string {
        return this.name;
    }
}
Prior art

- typescript-eslint · prefer-readonly

language/linter/src/rules/style/preferreadonly.rs:9