In a recent job interview, I was asked how does one detect (in a JavaScript function) whether a parameter actually had a value passed to it. It's been a long time since I've done any JavaScript, so I answered that I assumed there was a way to test for "null". The interviewer said that I had the appropriate concept, but the actual language keyword to test against was "undefined". We then had a brief discussion about null versus undefined, but I wanted to find out more.
Google turned up this page which has some very concise and useful examples. I was not amused, however, to read that testing for null will return true regardless of whether the value is actually null or undefined. I would hope that testing for undefined doesn't return true for null, and I hope to have time to test this sometime in the future. This brought me back to the first time I realized that JavaScript didn't (in previous incarnations, anyway) syntax check code that was never executed. I'm used to that happening for shell script, but it brought me up short for a language that actually seemed to be used in many shipping products.
I guess one works with what one is given, but it doesn't make me any more confident in JavaScript as a robust language.
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