instanceof usage in js

The instanceof operator is used to check whether an object is an instance of a class or its subclass. It returns a Boolean value indicating whether the object matches the given class or function.

Instanceof operator in JavaScript

Question: In JavaScript, instanceof operator What is the function of the talisman?

Answer: The instanceof operator is used to check whether an object is an instance of a class or its subclass.

Detailed description:

The instanceof operator has the following syntax:

<code>object instanceof constructor</code>

Among them:

• object is the object to be checked.
• constructor is the class or function to be compared. The

instanceof operator returns a boolean value:

• true: if object is a constructor instance or its subclass.
• false: If object is not an instance of constructor or a subclass thereof.

For example:

<code>const obj = new Array();
console.log(obj instanceof Array); // true
console.log(obj instanceof Object); // true
console.log(obj instanceof String); // false</code>

Application of instanceof operator:

The instanceof operator can be used in the following scenarios:

• Check the type of object.
• Verify the inheritance relationship of classes.
• Determine the return value type of the function.
• Implement polymorphic behavior.

Note:

• The instanceof operator only checks whether the object is an instance of a class or its subclass, not the actual contents of the object .
• The instanceof operator does not check prototype objects in the inheritance chain.
• Primitive values ​​(e.g. numbers, strings, booleans) are not instances of the class, so the instanceof operator will return false.

The above is the detailed content of instanceof usage in js. For more information, please follow other related articles on the PHP Chinese website!