Computed Properties and Watchers

Question 1

Describe the usefulness of computed properties

Answer 1

• In-template expressions are convenient, but are meant for simple operations that should only very few times in the template
  
  • Too much logic in the templates make them hard to maintain and read
• A template should be simple and declarative, not full of logic
• For complex logic, or logic that appears multiple times, computed properties should be used

Question 2

What is defining a computed property really doing?

Answer 2

• It’s using the function we define as the getter function for an automatically-created property of the same name

Question 3

Describe the difference between computed properties and methods.

Answer 3

• Computed properties are cached based on their dependencies
• Methods always run when a re-render happens
• Computed properties automatically update their bindings when a dependency changes
  
  • Methods do not, because they’re not properties

Question 4

Compare the styles of watch properties and computed properties

Answer 4

• Watch properties are imperative, and can be overly verbose
• Computed properties are terse, delcarative, and inheritantly watch all of the depdencies

Question 5

Describe computed setters.

Answer 5

• Computed properties getters-only by default.
• You can include a setter (set() {... ), if you need to also set the computed property (in essence setting it’s dependencies which will set the computed property)

Question 6

When is the best time to use a watcher?

Answer 6

When you want to perform asynchronous or expensive operations in response to changing data.