JAVASCRIPT

javascript check if not undefined

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

nodejs check if variable is undefined

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

}

javascript if a variable is undefined

if(typeof my_var === 'undefined') {
  //my_var is undefined
}

js check if undefined

let foo = undefined
//will return true
typeof foo === 'undefined'