Migrating JavaScript to TypeScript - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the first step when migrating a JavaScript project to TypeScript?

Rename your JavaScript files from .js to .ts to enable TypeScript features and start getting type checking.

beginner

Why add type annotations during migration?

Type annotations help catch errors early by telling TypeScript what kind of values variables and functions expect, making your code safer and easier to understand.

intermediate

What is the role of the tsconfig.json file in a TypeScript project?

It configures the TypeScript compiler options, like which files to include, target JavaScript version, and strictness rules, guiding how TypeScript checks and compiles your code.

intermediate

How can you gradually migrate a large JavaScript codebase to TypeScript?

Use the allowJs option in tsconfig.json to include JavaScript files, then convert files one by one, adding types step-by-step to avoid big disruptions.

beginner

What is the any type and when should you use it during migration?

The any type disables type checking for a variable. Use it temporarily when you don't know the exact type yet, but plan to replace it with specific types later.

What file extension should you use for TypeScript files?

A .js

B .ts

C .tsx

D .json

TypeScript files use the .ts extension. .tsx is for TypeScript with JSX.

Which tsconfig.json option allows JavaScript files to be included in a TypeScript project?

A includeJs

B jsSupport

C enableJs

D allowJs

The allowJs option lets the compiler process JavaScript files.

What does the any type do in TypeScript?

A Disables type checking for a variable

B Specifies a number type

C Defines a string type

D Creates a new type alias

any tells TypeScript to skip type checking for that variable.

Why is it good to add type annotations gradually during migration?

A To avoid breaking the whole project at once

B Because TypeScript requires all types upfront

C To make the code run faster

D To remove JavaScript files immediately

Gradual typing helps keep the project working while improving safety step-by-step.

What is the purpose of tsconfig.json?

A To install TypeScript packages

B To list all JavaScript files

C To configure TypeScript compiler options

D To run the TypeScript code

tsconfig.json tells the compiler how to process your TypeScript code.

Explain the main steps to migrate a JavaScript project to TypeScript.

Think about file changes, configuration, and adding types step-by-step.

Describe how the any type helps during migration and why it should be used carefully.

Consider both benefits and risks of using <code>any</code>.