check variable undefined code example

Example 1: js if not undefined

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

Example 2: checking if var is not defined js

if(typeof x !== 'undefined'){
  alert("Variable x is defined.");
}

Example 3: nodejs check if variable is undefined

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

}