How can I check whether a variable is defined in Node.js?

Question

I am working on a program in node.js which is actually js.

I have a variable :

var query = azure.TableQuery...

looks this line of the

Answer 1

Determine if property is existing (but is not a falsy value):

if (typeof query !== 'undefined' && query !== null){
   doStuff();
}

Usually using

if (query){
   doStuff();
}

is sufficient. Please note that:

if (!query){
   doStuff();
}

doStuff() will execute even if query was an existing variable with falsy value (0, false, undefined or null)

Btw, there's a sexy coffeescript way of doing this:

if object?.property? then doStuff()

which compiles to:

if ((typeof object !== "undefined" && object !== null ? object.property : void 0) != null) 

{
  doStuff();
}