MOCKSTACKS
EN
Questions And Answers

More Tutorials




How to detect if this dictionary key exists in Javascript?


javascript does key exist

var person={"name":"Billy","age":20}
person.hasOwnProperty("name"); // true
person.hasOwnProperty("sex"); // false

check if key does not exists in dictionary javascript

var person={"name":"Billy","age":20}
person.hasOwnProperty("name"); // true
person.hasOwnProperty("gender"); // false

javascript check if key exists in object

"key" in obj // true, regardless of the actual value

If you want to check if a key doesn't exist, remember to use parenthesis:
!("key" in obj) // true if "key" doesn't exist in object
!"key" in obj   // ERROR!  Equivalent to "false in obj"

Or, if you want to particularly test for properties of the object instance (and not inherited properties), use hasOwnProperty:
obj.hasOwnProperty("key") // true


Conclusion

In this page (written and validated by ) 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.