How to check if a function parameter is a Normalizr schema class?

Question

Is there any way to check, at runtime, if a function parameter is (or not) a Normalizr schema class? Could be any type: entity, array, object, etc.

For example:

function processTMDBRespose(response, schema) {
  // if 'schema' param is not a normalizr schema, throw!

  // some code
}

Answer 1

You can and can't do what you're looking for.

If you write yourself a lint rule that only allows creating schema from normalizr classes, like new schema.Array() and prohibits the use of shorthand [], then you can check using instanceof:

if (
    mySchema instanceof schema.Array || 
    mySchema instanceof schema.Entity ||
    mySchema instanceof schema.Object ||
    mySchema instanceof schema.Union ||
    mySchema instanceof schema.Values
) { 
    // your  code
} else {
    throw new Error('mySchema is not a schema');
}

However, if you use shorthand, any array [] or plain object {} is also a valid schema for schema.Array and schema.Object, respectively. This is much more difficult to validate, because almost everything is typeof Object in JavaScript (like null)