Jul 8, 2025 · A variable that has not been assigned a value is of type undefined. A method or statement also returns undefined if the variable that is being evaluated does not have an assigned value.

If it is undefined, it will not be equal to a string that contains the characters "undefined", as the string is not undefined. You can check the type of the variable:

Jul 11, 2022 · In this article, you will learn the various methods and approaches you can use to know if a variable is undefined in JavaScript. This is necessary if you want to avoid your code throwing errors …

Description The undefined property indicates that a variable has not been assigned a value, or not declared at all.

Jul 23, 2025 · In JavaScript, undefined is a primitive value that represents the absence of a value or the uninitialized state of a variable. It's typically used to denote the absence of a meaningful value, such …

Mar 31, 2024 · Unlike the reserved keyword null, undefined is a property of the global object. This was a design decision made early in JavaScript's development, and it let legacy browsers overwrite …

Summary: in this tutorial, you’ll learn about the JavaScript undefined and how to handle it effectively. If you have been working with other programming languages such as Java or C#, you may find that …

Aug 6, 2025 · Explore why JavaScript’s undefined isn’t a bug but a feature, and how understanding it changes the way you write and debug code forever.

3 days ago · Modern JavaScript Tutorial: simple, but detailed explanations with examples and tasks, including: closures, document and events, object oriented programming and more.

Dec 10, 2024 · As JavaScript has evolved from its loose dynamically-typed roots into complex front-end architectures, properly handling undefined values has become more important than ever before. In …