Function isA

isA<T extends Constructor>(value: unknown, ctor: T): value is InstanceType<T>
Generic type guard for instanceof checks.

This function provides a type-safe way to check if a value is an instance of a given constructor, with proper type narrowing for TypeScript. It combines the null/object check with instanceof to ensure the value is a valid object before performing the instance check.
Type Parameters
- T extends Constructor
  The constructor type to check against
Parameters
- value: unknown
  Value to test
- ctor: T
  Constructor function to check instanceof
Returns value is InstanceType<T>
true if the value is an instance of the constructor, false otherwise
Example
```
const obj = new Date();
if (isA(obj, Date)) {
  // obj is now typed as Date
  console.log(obj.getTime());
}
```
- Defined in src/guards.ts:294