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Resources & Documentation

Below are some common resources to assist you with your completion of this project. If you get stuck, start by consulting the following materials; if you have any additional questions, the course staff will be available to answer questions via Slack and Office Hours.

Git & GitHub Documentation

Documentation for working with Git and GitHub:

We also have a simple Git-based exercise that you are highly recommeneded to complete before proceeding with this project.

TypeScript Documentation

The repository README contains links to different documentation material that you may find helpful in your development process. Particularly, you will want to focus on the documentation relating to JavaScript/TypeScript:

You will also find some sample translated TypeScript files within the repository. You can use these as guidance for your translation process:

Additional TypeScript Background

This section provides more context on how TypeScript is used for this project and when it is appropriate to suppress ESLint warnings in your translated TypeScript files.

As native JavaScript does not have any typing, by default, all functions/values/classes/modules that are not typed will be automatically given the any type by TypeScript. Under default settings, this allows any valid JavaScript code to be run as TypeScript.

Using the any type, however, will defeat the purpose of the various type-checking features TypeScript provides. As such, we’ve set our linter to check for strict typing and disallow the use of the any type. For the most part, this should check that you explicitly type everything within your files and ensure that you are able to make the most out of TypeScript.

A limitation of this strictness is that there will be errors thrown when using non-translated JavaScript imports, which TypeScript will assume to have type any. As an example from one of our sample translated files src/social.ts:

// A module import from a non-translated JavaScript file database/index.js
import db from './database';

const activated = await db.getSetMembers('social:posts.activated');

Running the linter will give the following errors:

error  Unsafe member access .getSetMembers on an `any` value 

error  Unsafe call of an `any` typed value

error  Unsafe assignment of an `any` value

Let’s take a look at each error:

  • @typescript-eslint/no-unsafe-member-access - we don’t know the typing of our imported module db, so it is treated as any. However, we don’t know if something of type any has a function called getSetMembers, hence this is an unsafe member access
  • @typescript-eslint/no-unsafe-call - we don’t know the typing of the function db.getSetMembers, and so it is treated as any. We can not call a function of type any, so db.getSetMembers('social:posts.activated') is an unsafe call
  • @typescript-eslint/no-unsafe-assignment - we don’t know the return type of db.getSetMembers, and so it is treated as any. We can not assign something of type any to our variable activated

The first two errors are dependent on us knowing the typing of db and db.getSetMembers. However, because we haven’t translated the database/index.js file yet, we don’t have access to their typing information. In this case, it is okay to suppress the ESLint errors as they only arise from a lack of translation. We can do this by adding the following comments:

// The next line calls a function in a module that has not been updated to TS yet
// eslint-disable-next-line @typescript-eslint/no-unsafe-member-access, @typescript-eslint/no-unsafe-call
const activated = await db.getSetMembers('social:posts.activated');

For the last error, even though we don’t have typing information provided by the db module, we still want to make sure future uses of the activated variable get properly typechecked. Checking the rest of the file reveals that activated should be a string[] type; we can also manually cross-reference the db.getSetMembers function to check that this is the correct typing. Hence, it’s okay to cast the return value of this function call to string[], and our full solution looks like this:

// The next line calls a function in a module that has not been updated to TS yet
// eslint-disable-next-line @typescript-eslint/no-unsafe-member-access, @typescript-eslint/no-unsafe-call
const activated: string[] = await db.getSetMembers('social:posts.activated') as string[];

Installing Typing Packages

In some cases, if your file imports an npm package (such as lodash, nconf, etc), you will need to install the typings for the package. To do this, run:

% npm install @types/[packagename] --save-dev

You should then see the @types/[packagename] added to your package.json file.

GitHub Actions Packages

To make sure your GitHub Actions also install the correct packages, you should copy the package.json file to install/package.json.