using typeof on undefined javascript code example

Example 1: javascript typeof undfined

var x;
if (typeof x === 'undefined') {
   // these statements execute
}

Example 2: js this returns undefined

function foo() {
    console.log(this);
}

// normal function call
foo(); // `this` will refer to `window`

// as object method
var obj = {bar: foo};
obj.bar(); // `this` will refer to `obj`

// as constructor function
new foo(); // `this` will refer to an object that inherits from `foo.prototype`