Function hasJsonMap

Tests whether a value of type T extends AnyJson contains a property key of type JsonMap. If so, the type of the tested value is narrowed to reflect the existence of that key for convenient access in the same scope. Returns false if the property key does not exist on the object or the value stored by that key is not of type JsonMap.

// type of obj -> unknown
if (hasJsonMap(obj, 'body')) {
  // type of obj -> { body: JsonMap }
}
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