In this workshop, you will:

• learn how to use and translate between three asynchronous concepts in TypeScript
• understand how asynchronicity impacts ordering of code execution
• learn how to test asynchronous code

A reference solution is found on the solution branch. We recommend you practice this exercise without AI tools -- it's meant to help you learn!

The exercises for you to complete are specified below. Please check in with your TA to discuss your answers once you are done!

This workshop uses the same tooling as the project. In order to participate, you will need to have your machine setup for development. If you haven't already, please download the tools specified in the ReadMe of your project repository (e.g. nodejs, yarn).

These are specified in package.json if you are curious or want to edit!

Installing Packages

yarn install

Build

yarn build

Run Script

yarn execute

Test

yarn test

The code you will be writing identifies lines from movie scripts that contain keywords.

This function is defined in src/readfile.ts. You can run it with the following command:

yarn execute

Question 0.A: In plain English, what does this function do? Is the provided JSDoc comment complete? If not, add the missing information to the JSDoc.

Question 0.B: Do the results of the console.log and the return value of the function match up? Why not? In your explanation, reference the possible orders of executions of the annotated lines of code.

Using fs.promises.readFile(), fill in logLinesWithKeywordPromise so that it behaves the same as logLinesWithKeywordCallback but uses the Promise syntax (using .then()) and verify it by modifying and running src/index.ts.

Question 1.A: Which version do you like better (or do you like them about the same)? Why?

Question 1.B: Does the bug from 0.B still exist? Why? In your explanation, reference the possible orders of executions of the lines of code.

Now, using async/await syntax, fill in logLinesWithKeywordAwait and verify it works by modifying and running src/index.ts.

Question 2.A: Which version do you like better (or do you like them all about the same)? Why?

Question 2.B: Does the bug from 0.B and 1.B still exist? Why or why not? In your explanation, reference the possible orders of executions of the lines of code.

Using async/await makes it easier for us to return values and actually use them! Now we will try to do something useful with the results! Instead of logging the lines and returning the count, we just want to return all the lines. If the function is successful, it should return a Promise containing the appropriate lines, and if it is unsuccessful, it should return a rejected promise that says "Error!!".

Task 3.A: Fill in getLinesWithKeyword (hint: it will be very similar to part 2's code!). Remember to fill in the return type annotation for the function signature!

Task 3.B: Write tests for the successful execution case in test/readfile.spec.ts. You can run tests with the command yarn test!

Task 3.C: A test already exists for the error case. It's a bit confusing why the test is written in the way that it is. Why is it written like that? Leave your thoughts in a comment that will help you and other developers when they come across it!

Task 3.D: Modify the code and test case to return a better error message!

Now we want to extract keywords from all the movie scripts in a directory (skipping any file that does not contain "-script" in it). You will learn how to do this two ways (only one of them is the preferred way!).

Task 4.A: Write getAllKeywordLinesSlow, which executes getLinesWithKeyword using await in a loop.

Task 4.B: Write getAllKeywordLines which executes getLinesWithKeyword using Promise.all().

Task 4.C: Write a new test for getLinesWithKeyword. One is already provided for you!

Task 4.D: getAllKeywordLines is the preferred version. Why do you think that is?

Hint: you should use fs.promises.readdir()!

Once you have completed all the questions and tasks through Task 4.D, raise your hand and a TA will discuss your answers with you and check you off!