# Migration to v4.X and higher

This guide assists developers in migrating from Flagship 3.X to Flagship 4.X and higher.

The primary changes include:

* Asynchronous Flagship.start
* Visitor Creation options
* Flagship configuration
* Renamed Types and APIs

For more details, see the [change log](https://github.com/flagship-io/flagship-ts-sdk/releases)

## Asynchronous Flagship.start

In version 5.X and higher, The `Flagship.start` method is now asynchronous and returns a Promise. You may need to update your code to properly await initialization before accessing flags or creating visitors.

{% tabs %}
{% tab title="Now" %}

```typescript
// New version - asynchronous
const flagship = await Flagship.start('ENV_ID', 'API_KEY', {
    // config options
  });

  // Now you can safely use the SDK
const visitor = flagship.newVisitor({
    visitorId: 'visitor-id',
    hasConsented: true
});
```

{% endtab %}

{% tab title="Before" %}

```typescript
// Previous version - synchronous
const flagship = Flagship.start('ENV_ID', 'API_KEY', {
  // config options
});

// Immediately use the SDK
const visitor = flagship.newVisitor({
  visitorId: 'visitor-id',
  hasConsented: true
});
```

{% endtab %}
{% endtabs %}

## Visitor Creation options

In version 4.X and higher , when creating a visitor, the [hasConsented](/server-side/sdks/js-sdk/js-reference.md#hasconsented-property) option is now required. In contrast, this option was optional in version 3.X. Additionally, the `isNewInstance` option has been replaced with [shouldSaveInstance](/server-side/sdks/js-sdk/js-reference.md#visitor-class), `onFetchFlagsStatusChanged` has been renamed to [onFlagsStatusChanged](/server-side/sdks/js-sdk/js-reference.md#onflagsstatuschanged)

Below is an example of how consent is used in versions 4.X and 3.X

{% tabs %}
{% tab title="Now" %}

```typescript
const fsVisitor = Flagship.newVisitor({
  hasConsented: true, // This is now mandatory
});
```

{% endtab %}

{% tab title="Before" %}

```typescript
const fsVisitor = Flagship.newVisitor();
```

{% endtab %}
{% endtabs %}

## Flagship configuration

In version 4.X and higher, the `enableClientCache`option of [IFlagshipConfig](/server-side/sdks/js-sdk/js-reference.md#sdk-configuration) has been replaced with [reuseVisitorIds](doc:js-reference#sdk-configuration) and the `statusChangedCallback` has been replaced with [`onSdkStatusChanged`](/server-side/sdks/js-sdk/js-reference.md#onsdkstatuschanged).

## Renamed Types and APIs

### Flag Status

In the version **5.x** and higher, the `FetchFlagsStatus` type has been renamed to `FlagsStatus` for clarity.

### Flagship SDK Status

The `FlagshipStatus` enum has been superseded by [`FSSdkStatus`](/server-side/sdks/js-sdk/js-reference.md#fssdkstatus).

The table below matches the `FlagshipStatus` enum keys from version 3.X to the corresponding [`FSSdkStatus`](/server-side/sdks/js-sdk/js-reference.md#fssdkstatus) keys in version 4.X and higher.

| V4.X                  | V3.X             |
| --------------------- | ---------------- |
| SDK\_NOT\_INITIALIZED | NOT\_READY       |
| SDK\_NOT\_INITIALIZED | NOT\_INITIALIZED |
| SDK\_INITIALIZING     | STARTING         |
| SDK\_INITIALIZING     | POLLING          |
| SDK\_PANIC            | READY\_PANIC\_ON |
| SDK\_INITIALIZED      | READY            |

\\

## `GetFlag` method update

In version 4.X and higher, the approach to setting a flag's default value has been modified. The default value is no longer set using the [getFlag](/server-side/sdks/js-sdk/js-reference.md#getflag-method) method of visitor instance. Instead, it is now set using the [getValue](/server-side/sdks/js-sdk/js-reference.md#getvalue-method) of [flag](/server-side/sdks/js-sdk/js-reference.md#ifsflag-interface) instance.

Here's how you can retrieve the default value of a flag in versions 4.X and 3.X:

{% tabs %}
{% tab title="Now" %}

```typescript

...

const flag = fsVisitor.getFlag("myFlagKey");
const flagValue = flag.getValue("default-value");
```

{% endtab %}

{% tab title="Before" %}

```typescript

...

const flag = fsVisitor.getFlag("myFlagKey", "default-value");
const flagValue = flag.getValue();
```

{% endtab %}
{% endtabs %}


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