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

For easy tasks I often simply do it like:

var undef;

// Fails on undefined variables
if (query !== undef) {
    // variable is defined
} else {
    // else do this
}

Or if you simply want to check for a nulled value too..

var undef;

// Fails on undefined variables
// And even fails on null values
if (query != undef) {
    // variable is defined and not null
} else {
    // else do this
}