There are two different syntaxes, dot notation and bracket notation. Dot notation is generally preferred for readability but properties must be a valid identifier.
Here is how using dot notation:
myDog.bark = "woof-woof";
Here is how using bracket notation:
myObject['bark'] = "woof-woof";
Using bracket notation, we can utilize variables as property names:
var dynamicProperty = "bark"; myObject[dynamicProperty] = "woof-woof";