[陷阱]console.log("This is a string." instanceof String); // false

 console.log("This is a string." instanceof String); // false

This actually returns false.

The reason for that circumstance is that JavaScript distinguishes between primitives and objects.

And "This is a string." is actually a primitive string and not an instance of the object String.

If the code was like this:

new String("This is a string.") instanceof String

you'd actually get the result you would have expected at the beginning.

What instanceof actually does is checking if the String constructor is nested within the prototype chain of the value provided.

In this case, it isn't.