Lets first look at Dot notation. Consider this example below:
let obj = {
  cat: 'meow',
  dog: 'woof'
};
let sound = obj.cat;
console.log(sound);
// meow
I want to bring your attention to the fifth line where we’re using dot notation: let sound = obj.cat;. This is an example of dot notation. You can access properties on an object by specifying the name of the object, followed by a dot (period) followed by the property name. This is the syntax: objectName.propertyName;.
When working with dot notation, property identifies can only be alphanumeric (and _ and $). Properties can’t start with a number.