# Migration (v6 to v7) (/docs/migration-v6-to-v7)



v7 is a major release. The decorator surface changed. Everything else (the `Envapter` readers, converters, sources, and types) is unchanged and stays on `envapt`.

## Decorators are now TC39 accessor decorators [#decorators-are-now-tc39-accessor-decorators]

The default `@Envapt` import, and the sugar decorators, is now a TC39 Stage 3 accessor decorator. It needs no `experimentalDecorators` flag and runs on any runtime, including Bun and Deno executing a `.ts` file directly.

Declare the field with the `accessor` keyword. Static fields use `static accessor x: T`, instance fields use `accessor x!: T` with the definite-assignment `!`.

```ts
// v6 (legacy form)
import { Envapt, Converters } from 'envapt';

class Config {
    @Envapt('PORT', { converter: Converters.Number, fallback: 3000 })
    static readonly port: number;
}

// v7 default (accessor form, no experimentalDecorators)
import { Envapt, Converters } from 'envapt';

class Config {
    @Envapt('PORT', { converter: Converters.Number, fallback: 3000 })
    static accessor port: number;
}
```

For an instance field, the change is from `declare readonly x: T` to `accessor x!: T`.

## Keeping the legacy decorators [#keeping-the-legacy-decorators]

If you cannot switch to the accessor form yet, the v6 decorators move to the `envapt/legacy` subpath. They keep the `static readonly` / `declare readonly` form and still need `experimentalDecorators`.

```ts
// keep the v6 behavior
import { Envapt, Converters } from 'envapt/legacy';

class Config {
    @Envapt('PORT', { converter: Converters.Number, fallback: 3000 })
    static readonly port: number;
}
```

Only the decorators move. `Envapter`, `Converters`, the sources, and the types stay on `envapt`. A module that imports decorators only from `envapt/legacy` must also `import 'envapt'` once so the runtime source binds.

## Decorated properties are read-only [#decorated-properties-are-read-only]

Assigning to a decorated property now throws `EnvaptError`. Till v6 the legacy decorator installed only a getter, so an assignment was a silent no-op in sloppy mode or a native `TypeError` in strict mode. Both the default and legacy forms throw the clearer error in v7.

## Decorated fields are typechecked [#decorated-fields-are-typechecked]

The decorator checks the decorated field's declared type against the converter's output. A field that cannot hold the value is a compile error, `[envapt] field type must hold the converter output`. A no-fallback read can be `null`, so a field that compiled as `static readonly port: number` for `@EnvNum('PORT')` on v6 now needs `number | null` (or `static accessor port: number | null` in the modern form). This check applies to both the modern and legacy decorators.