When an object is converted to a string, it displays in a standard way as either '[object Object]', or '[object Array]' if it is an array. The [Symbol.toStringTag] computed property customizes the string shown after object, so that the object converted to string displays as '[object <customized string>]'. For instance, it is possible to customize the Person class so that it displays as '[object Person]':
export class Person { ... get [Symbol.toStringTag]() { return "Person"; } ... } let anObject: any = new Person("Francesco", "Abbruzzese"); // shows [object Person] alert(anObject);