```javascript
WXAPI.checkReferrer(referrer)
```
+ referrer user ID
This interface is used to verify the validity of the invitation code and prevent users from entering a wrong invitation code casually.
Valid:
```json
{
"code": 0,
"msg": "success"
}
```
Does not exist:
```json
{
"code": 700,
"msg": "No data yet"
}
```