Improve error message when inserting a list into a mixed property

[kraenhansen]

Goals

Clear and actionable error messages.

Expected Results

An error message such as:

A mixed property doesn't support lists of values

Actual Results

The following error is thrown:

Error: Only Realm instances are supported.

Steps to Reproduce & Code Sample

1. Open a Realm with a schema declaring a mixed property.
2. Try inserting a list of values

const realm = new Realm({
  schema: [{
    name: "MixedClass",
    properties: { value: "mixed" },
  }],
});
realm.write(() => {
  realm.create("MixedClass", { value: [123, false, "hello"] });
});

Version of Realm and Tooling

• Realm JS SDK Version: 10.5.0-beta.1
• Node or React Native: Tested on Node.js
• Client OS & Version: N/A
• Which debugger for React Native: None

[davidaharlow]

Same For Me with 10.5.0 (not beta) on ReactNative

Expected:
A mixed property doesn't support lists of values

Actual:
Error: Only Realm instances are supported.

Version of Realm and Tooling
Realm JS SDK Version: 10.5.0
Node or React Native: Tested on React Native
Which debugger for React Native: Flipper

[kneth]

The reason is that we have a late type deduction for Mixed values, and the code path followed in this case is that array is interpreted as an object (which is a link when it is stored in Realm) since Array is also an Object in JavaScript.

We should put in an earlier check to guard against array and other not support types.