JAVASCRIPT

js isset

if (typeof obj.foo !== 'undefined') {
  // your code here
}

js isset variable

if (obj.hasOwnProperty('foo')) {
  // your code here
}

check if isset variable js

var status = 'Variable exists'

try {
  myVar
} catch (ReferenceError) {
  status = 'Variable does not exist'
}

console.log(status)