how to check if a variable is not undefined in javascript code example

Example 1: js if not undefined

if (typeof myVar !== "undefined") {
    console.log("myVar is DEFINED");
}

Example 2: nodejs check if variable is undefined

if ( typeof query !== 'undefined' && query )
{
  //do stuff if query is defined and not null
}
else
{

}

Example 3: How can I check whether a variable is defined in Node Js

if (query){
   doStuff();
}