Type Hierarchy

All the types in TypeScript can be arranged into a hierarchy of sorts. I've drawn one below:

Obviously I didn't list every type, but the goal here is to show you how narrowing works in TypeScript, and why you should care. Some key points:

• The types at the top of hierarchy are the "widest". They encompass the most possible values, and very little is known about them.
• The types at the bottom of the hierarchy are the "narrowest". They encompass the fewest possible values, and a lot is known about them.
• any and unknown are at the top of the hierarchy, the weird one is actually the any type, because it just breaks all the rules, allowing you to do whatever you want with it.
• never is at the bottom of the hierarchy, because it represents values that can't occur.
• Types below are assignable to the connected types above them, but not the other way around. For example:
  • "armin" is assignable to "armin" | "eren" which is assignable to string which is assignable to any.
  • "armin" | "eren" is not assignable to "armin" because what would happen if the value happened to be "eren"?
• Interestingly, undefined and null are assignable to void (at least, when strictNullChecks is disabled), but not the other way around.

Assignment

Our AI magic™ uses sentiment analysis to algorithmically deduce whether user feedback is positive or negative.

1. Complete the respondToSentiment function:
   1. If the input is positive, pass it to handlePositiveSentiment and return the result.
   2. If the input is negative, pass it to handleNegativeSentiment and return the result.
   3. If the input is anything else:
      1. Return the message "We don't understand."
      2. Notify the manager
2. Complete the handlePositiveSentiment function:
   1. If the input is "happy":
      1. The response message should be "Hooray!"
      2. Don't notify the manager
   2. If the input is "satisfied":
      1. The response message should be "We are glad."
      2. Don't notify the manager
3. Complete the handleNegativeSentiment function:
   1. If the input is "dissatisfied":
      1. The response message should be "We are sorry."
      2. Don't notify the manager
   2. If the input is "angry":
      1. The response message should be "We apologize. A manager will contact you."
      2. Notify the manager