undefined
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What is undefined?
undefined is the default value of a variable that has been declared but not assigned a value. It is also the return value of functions that do not explicitly return anything. Unlike null, which is intentionally empty, undefined typically indicates something has not been set.
Free resources to learn undefined
- Articleundefined - JavaScript | MDN
- Videoundefined in JS
More in stage 3: Data Types
undefined: common questions
Can I learn undefined in Hindi?
This lesson is written in English. Once you sign in, open it in the interactive course and ask the AI tutor to explain undefined in Hindi or Hinglish. The tutor answers from this lesson’s own text, so it stays on the syllabus, and it runs on your own Google, OpenAI or Anthropic key.
Is this undefined tutorial for beginners?
It is lesson 23 of 124 in the free JavaScript roadmap, in stage 3, Data Types. If you are new to JavaScript, start from stage 1 and come back here in order; if you already know the earlier stages, this lesson stands on its own.