$slice

Update records by extracting a specified portion of an string in a column. The $slice method is used to select a subset of elements from a segment of characters from a string, based on the provided start index and length. This is useful for working with arrays or strings where only part of the data needs to be modified or retrieved.

await Member.$update({
    $where: { 
        age: { 
            $eq: 16 
        } 
    },
    $update: {
       $slice: {
         username: { $begin: 1, $end: 5 }
       }
    }
});