Rubo's Blog

NaN is the only value in Javascript that is not equal to anything, including itself.

if(NaN !== NaN){
  alert("what??? how???  huh???");
}

Therefore, one way you could check if a variable has the value of NaN is to do something like this:

if(yourVar !== yourVar) { // thanks Vigen Sarksyan for this suggestion
  alert("yourVar has a value of NaN");
}

While this will work, it is not recommended as most people will think you wrote this by mistake and assume there is a bug in your code. The correct way to check if a variable contains a NaN is by calling the isNaN function:

if(isNaN(yourVar)) {
  alert("yourVar has a value of NaN");
}

This is much more readable and produces the same result.

Also note the fact that while NaN stands for “Not a Number”, calling typeof(NaN) returns “number”…so it’s a number that is not a number 🙂

Deleting values from beep nested array by calling the ‘update’ function can be tricky to get right when using MongoDB. Suppose you have this structure:

{
  _id: 'someID',
  foo: [
    {
      bar: [
        {
          title: 't1'
        },
        {
          title: 't2'
        }
      ]
    },
    {
      bar: [
        {
          title: 't3'
        },
        {
          title: 't4'
        }
    }
  ]
}

Now suppose we want to remove the object with title ‘t1’ from the array it is in. I first tried doing this:

 db.myCollection.update({ _id : 'someID' },
                        { $pull : { 'foo.bar' : { 'title' : 't1' } } }); 

However, this did not seem to work. Adding a ‘.$’ after foo seemed to do the trick:

 db.myCollection.update({ _id : 'someID' },
                        { $pull : {'foo.$.bar' : { 'title' : 't1' } } });

I hope this saves you some time. Good luck!