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Livecoding.tv Quiz of the Day: 05/10/2016

quiz-of-the-day-pitfall-1

Answer

Although typeof bar === “object” is a reliable way of checking if bar is an object, the surprising gotcha in JavaScript is that null is also considered an object!

Therefore, the following code will, to the surprise of most developers, log true (not false) to the console:

As long as one is aware of this, the problem can easily be avoided by also checking if bar is null:

To be entirely thorough in our answer, there are two other things worth noting:

First, the above solution will return false if bar is a function. In most cases, this is the desired behavior, but in situations where you want to also return true for functions, you could amend the above solution to be:

Second, the above solution will return true if bar is an array (e.g., if var bar = [];). In most cases, this is the desired behavior, since arrays are indeed objects, but in situations where you want to also false for arrays, you could amend the above solution to be:

Or, if you’re using jQuery:

If you want to explore other questions about JavaScript, you can check our videos section! Below we have some examples:

You can also subscribe to some channels that broadcast in JavaScript, such as the following:

challenge coding JavaScript programming quizjessered

challenge coding JavaScript programming quizgunn4r

Another cool way to find out interesting things about JavaScript is to access our project page!

About author

I, Dr. Michael J. Garbade is the co-founder of the Education Ecosystem (aka LiveEdu), ex-Amazon, GE, Rebate Networks, Y-combinator. Python, Django, and DevOps Engineer. Serial Entrepreneur. Experienced in raising venture funding. I speak English and German as mother tongues. I have a Masters in Business Administration and Physics, and a Ph.D. in Venture Capital Financing. Currently, I am the Project Lead on the community project -Nationalcoronalvirus Hotline I write subject matter expert technical and business articles in leading blogs like Opensource.com, Dzone.com, Cybrary, Businessinsider, Entrepreneur.com, TechinAsia, Coindesk, and Cointelegraph. I am a frequent speaker and panelist at tech and blockchain conferences around the globe. I serve as a start-up mentor at Axel Springer Accelerator, NY Edtech Accelerator, Seedstars, and Learnlaunch Accelerator. I love hackathons and often serve as a technical judge on hackathon panels.