check if variable is defined javascript code example

Example 1: javascript check if variable exists

if (typeof myVar !== 'undefined') {
    // myVar is defined
}

Example 2: check if isset variable js

var status = 'Variable exists'

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

console.log(status)

Example 3: How can I check whether a variable is defined in Node Js

if (query){
   doStuff();
}