What will be the output of the code below?

var x = { foo : 1};
var output = (function(){
   delete x.foo;
   return x.foo;
  })();

console.log(output);


Answer:

The above code will output the following to the console:

undefined


The delete operator is used to delete the property of an object.
Here, x is an object which has the property foo, and as it is a self-invoking function, we will delete the foo property from object x.
After doing so, when we try to reference a deleted property foo, the result is undefined.