Post History

In javascript is there really a good reason to never check for boolean true || false such as if(var){}else{}?

I am fairly certain this isn't a duplicate so please bear with me.

I check for boolean true||false using if() as a matter of course in my programming. I've programmed extensively in PHP, some in C# ASP.NET, a bit in Java, a long time ago in C++, & dabled in a few others. Checking for boolean true||false has always been pretty straightforward (as far as I could tell). But in JavaScript I've heard, read, and otherwise been told it's bad. That instead of:

    if(var){}else{}
I should instead do:

    if(typeof(var) !== 'undefined' || typeof(var) !== null || var !== ''){}else{}

Previous to the six months prior to asking this question (originally on StackOverflow) I was a dabbler in JavaScript. After getting tired of writing & re-writing the long version of the boolean test shown above I finally asked a friend who's done extensive js development for years. My friend supported what I'd read, that I should never test for boolean true or false the way I'm used to. However, after that discussion I have a stronger belief that if(var){}else{} IS actually completely fine in js as it works EXACTLY like I would intuitively expect it to ([my jsfiddle testing this][1])

I've looked around and found various links. The following seemed to be the more relevant:

 - [Most relevant an article on the good blog javascriptweblog (Angus
   Croll)][2] 
 - [A kind of similar question on stackoverflow (which
   to my mind was obvious... checking for a boolean value vs an equality
   check...)][3]
 - [Another question very similar to the above on
   stackoverflow][4]

The thing that convinced me most that my usage is safe and will work fine is the 3rd answer to the first SO question I linked to above given by Incognito. The js spec is very clear about what will & will not evaluate to boolean true||false, and again this is exactly as I would have expected (though have to be reminded that an empty array is an object... but that is specific to JavaScript, while the rest of it is exactly as I would expect). 

Can someone please provide a definitive reason to not check for boolean true or false in JavaScrpt, realizing I know the difference between a boolean check and an equality check??

Thanks in advance!

  [1]: http://jsfiddle.net/mrummler/yo2h7njm/
  [2]: https://javascriptweblog.wordpress.com/2011/02/07/truth-equality-and-javascript/
  [3]: https://stackoverflow.com/questions/7615214/in-javascript-why-is-0-equal-to-false-but-when-tested-by-if-it-is-not-fals
  [4]: https://stackoverflow.com/questions/7496727/why-does-0-a-b-behave-different-than-0-true-a-b?lq=1