undefined are both primitive values.
undefined variable is a variable that has been declared but doesn’t have a value assigned (yet).
For example, try logging the following variable:
undefined because the
dogBreed variable has no value.
null is a value that is commonly assigned to a variable. For example, to avoid having an undesired undefined variable in your code, you can assign the value
null to that variable (and give it a real value later):
let dogBreed = null
null is evaluated as an object, which the following code shows: