check if a var is undefined in javascript code example

Example 1: javascript check if undefined or null

// simple check do the job
if (myVar) {
 // comes here either myVar is not null,
 // or myVar is not undefined,
 // or myVar is not '' (empty string).
}

Example 2: How can I check whether a variable is defined in Node Js

if (query){
   doStuff();
}