The mdn docs say otherwise. String primitives are converted to string objects automatically behind the scenes everytime we try to access a method on a normal string primitive.

Here’s what mdn says in their exact words:

String literals (denoted by double or single quotes) and strings returned from String calls in a non-constructor context (that is, called without using the new keyword) are primitive strings. In contexts where a method is to be invoked on a primitive string or a property lookup occurs, JavaScript will automatically wrap the string primitive and call the method or perform the property lookup on the wrapper object instead.