/Javascript/Node.js/Nodejs check if variable is undefined

Nodejs check if variable is undefined

Javascript check if not undefined

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

Javascript if undefined

if(typeof comment === 'undefined') {

  alert('Variable "comment" is undefined.');

} else if(comment === null){

  alert('Variable "comment" is null.');

}

Source: tutorialrepublic.com

Js check if undefined

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

Nodejs check if variable is undefined

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

}

Source: stackoverflow.com

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