Function assertRecord

assertRecord<T>(
value: T,
errorMsg?: string,
): asserts value is T & Record<string, unknown>
Asserts that a value is a non-null, non-array object that can be treated as a string-keyed record.

Unlike isRecord, this function does not narrow the value to a generic indexable structure. Instead, it preserves the existing static type of the variable. This makes it ideal for validating option objects or interface-based inputs where all properties may be optional.

Use this function when:
```
  - You need to reject `null`, primitives, or arrays at runtime.
  - You want to safely treat the value as a record, **without losing its compile-time shape**.
```
Type Parameters
- T
Parameters
- value: T
  The value to validate.
- OptionalerrorMsg: string
  Optional message used for the thrown TypeError.
Returns asserts value is T & Record<string, unknown>
Example
```
interface Options { flag?: boolean; value?: number; }

function run(opts: Options = {}) {
  assertPlainObject(opts, `'opts' is not a record object.`);   // `opts` remains `Options`, not widened or reduced.
  opts.value;                                                  // Fully typed access remains available.
}
```
Throws
if the value is null, non-object, or an array.