Why will an error be reported without adding instanceof?

The reason is: The instanceof operator is used to check whether an object is an instance of a specific class (or its derived class). If the object is not an instance of a class, then type determination cannot be made and an error is thrown. To avoid this error, when using the instanceof operator, you need to ensure that the object is an instance of a class. If you are not sure about the type of an object, you can use other methods to determine the type.

Operating system for this tutorial: Windows 10 system, Dell G3 computer.

In JavaScript, if you try to use the instanceof operator on an object that is not an instance of a class, a TypeError will be thrown.

This is because the instanceof operator is used to check whether an object is an instance of a specific class (or its derived class). If the object is not an instance of a class, then type determination cannot be made and an error is thrown.

The following is an example:

const obj = { name: "John" };console.log(obj instanceof Object); // trueconsole.log(obj instanceof Array); // false，抛出 TypeError 错误

In the above example, obj is an ordinary object, it is not an instance of the Array class. Therefore, using obj instanceof Array will throw a TypeError error.

In order to avoid this error, when we use the instanceof operator, we need to ensure that the object is an instance of a class. If you are not sure about the type of an object, you can use other methods to determine the type, such as using the typeof operator or other type checking methods.

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