How to Check if a Variable Is Undefined in Javascript?

test if is undefined javascript

let id;

if(typeof id === 'undefined') {
    console.log("id is undefined...");
}

check if variable is undefined

if ( typeof query !== 'undefined' && query )
{
  //do stuff if query is defined and not null
}
else
{

}

Conclusion

In this page (written and validated by A. Gawali) you learned about . What's Next? If you are interested in completing Javascript tutorial, we encourage you simply to start here: Javascript Tutorial.

Incorrect info or code snippet? We take very seriously the accuracy of the information provided on our website. We also make sure to test all snippets and examples provided for each section. If you find any incorrect information, please send us an email about the issue: mockstacks@gmail.com.

Share On:

Mockstacks was launched to help beginners learn programming languages; the site is optimized with no Ads as, Ads might slow down the performance. We also don't track any personal information; we also don't collect any kind of data unless the user provided us a corrected information. Almost all examples have been tested. Tutorials, references, and examples are constantly reviewed to avoid errors, but we cannot warrant full correctness of all content. By using Mockstacks.com, you agree to have read and accepted our terms of use, cookies and privacy policy.