Moving From JavaScript to TypeScript: Things Developers Should Know

Moving From JavaScript to TypeScript:
Things Developers Should Know
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You must have heard that typescript is the superset of Javascript, it is because
all Javascript code is valid for typescript as well. But, the added benefit of
typescript is that it offers easier detection of errors before execution, which is
absent in Javascript.
Let’s say you have started a project in javascript and it needs to be migrated to
typescript. But you have come so far in your project that starting from zero in
typescript will be tedious. So, in this article, we will discuss why developers still
go with typescript for the completion of their project. Before diving, let's
understand why you should use typescript.

Why should you use typescript?
Some features of typescript like function with REST parameters and optional
parameters, generic and modules support to compel the user to use it. Using
typescript will make the JS code more efficient by making its code easier to
read and debug, thus find errors easily. So, developers get ready to save your
time. Below, you can find reasons why TypeScript is becoming famous among
developers.
1. Strong static typing
In Javascript, datatype errors are spotted only at runtime but typescript offers
strong static typing. Here, once you declare, a variable doesn’t change its type.
The compiler gives heads-up about the type-related mistakes. It gives a better

Typescript doesn’t force developers to declare types everywhere and gives
them to freedom to change the level of type strictness in different levels of a
project.
2. Early Detection of Bugs
Typescript finds bugs at the compile stage which saves a lot of time for a
developer. It allows them to spend time correcting logic rather than catching
common mistakes.
3. Fast Refactoring
In typescript, refactoring multiple files at a time is painless. If you want to
improve your app, rename the components, change the object; it will keep your
codebase robust. Typescript spots the bugs so it will simplify the refactoring.

With IDEs commands, you will be able to use navigation tools like “find all
references” or “go to definition.”
4. Reduced Boiler Plate Tests
Typescript assures the passing of correct variables into the correct places, so
you won’t be distracted to test them all. It gives you more time to focus on app
logic than writing integration test cases.
5. Supports Rich IDEs
Typescript supports rich Integrated development environments (IDE) that
ensure a boost in the productivity of a developer. These IDEs provide features
such as autocompletion, auto navigation, and suggestions so that developers
can write robust and maintainable code.

Now, we know why developers would be interested to move from JavaScript to
Typescript, let’s see how does the process look like.
Moving from Javascript to Typescript
The good part is that if you know javascript, you already know much about
typescript. Typescript files have .ts or .tsx as extension. Browsers don’t
acknowledge typescript, so its code is compiled to plain javascript code. Now
let’s start the main steps:
1. Placing your directories:
The part of your project that you’ve written in JS must have .js files in lib, src, or
dist directory. These files will be used as inputs in typescript to run the output
you desire.

While migrating from JS to typescript, separate input files will be needed to
prevent Typescript from overwriting them. There will be an output directory for
the output files if they need a specific directory for storage.
If you’re executing some intermediate steps on JS like bundling or working with
a transpiler like Babel, then you already have a folder like this setup.
Check if you have a tests folder outside of the src directory. If it is true, then
there will be 2 tsconfig.json, one in src and another in tests.
Here are some references for the keywords used:
With includes: Reading files in the src directory.
With allowJS: Receive JS files as inputs.

With outDir: Discharge output files in-built.
2. Placing Typescript
Tsc is a compiler that compiles the typescript code for browsers to understand
it. There are two ways of doing it:
● Being part of react project:
You can use CRA(create-react-app) tools to build a new project in React
configured with TypeScript.
npx create-react-app my-app --template typescript
(OR)

There is no special configuration needed like editing a tsconfig.json file as
everything is done by CRA tools. Just run the project as we run react project.
● Being part of npm project:
Once the last step is executed, the tsconfig.json file is generated which is
stored in the root directory of the project. It has options and settings stored for
the tsc compiler.
We will make a separate src directory for our typescript files and a dist directory
for javascript files.
"
mkdir src dist

Open your project in the code editor and write these two lines in the
tsconfig.json file:
“outDir”: “./disc”
“rootDir”: “./src”
This will tell tsc where JS files are placed and where to find TS files.
The common property of tsconfig.json is ComplileOptions. It is an object which
is used to change the method through which TypeScript transcript files in JS. It
can be done by setting its value to TRUE.
For example: in CompileOptions, if noImplicitAny: true and strictNullChecks:
true, then it is a sign of confirmation that our .ts files will check for “types”.

3. Start moving to Typescript files
There is no need to migrate all the JS files. You can keep those you want in JS
format. You can start by renaming your JS files or changing the extension from
.js to .ts or .tsx(if you are using JSX). When you open a newly built file in code
editor that supports TypeScript, you may come across some errors. Try to
resolve those errors keeping in mind the TypeScript features.
A common error: “cannot find a module”
This is a very common error that you may face which points to some modules
that might be missing in your import statements.

Simplifying, it refers to modules that are not defined in the declaration file of the
project. To resolve them, you’ll have to install those missing modules using the
prefix “@types”.
@types is the package name or a customized version of a package for
typescript. For instance: If an error pops up “React is missing”, then you can
install @types/react by:
npm install --save-dev @types/react
Types
In JS, a variable type is determined dynamically during runtime. One benefit of
typescript is assigning types to variables. It enhances the readability of the
code and thus reduces the chances of bugs.

Remember the given remarks while assigning values to variables:
“Any” type: it points to dynamic type. It is similar to removing typechecking for a
variable.
“Null or undefined:” if any variable in your code is null or undefined, then we
can explicitly tell that it isn’t with an exclamation mark.
Some common examples of type include “number”, “string”, and “boolean”.
4. Adding properties to an object:
But using the same code in Typescript will show errors like name and age
property don’t exist in parent variable having the type {}.

Or these can be defined in separate interfaces.
Advantages of Typescript over Javascript
To assure you of the decision of moving from JS to typescript here are some
advantages:
● With typescript, you can use highly productive development tools like static
checking for JS IDEs and practices.
● To support the latest browser, you can compile the typescript code
according to ES5 and ES6 standards.
● Typescript is structural and not nominal, so developers get ready to save
your time.
● You can enjoy all benefits of ES6(ECMAScript 6), thus more compatibility

By type checking the code, developers can avoid tedious bugs which otherwise
would be difficult in JavaScript.
Final thoughts
Moving from javascript to typescript is not that tedious if you follow the proper
steps since every JS code is a valid typescript code. You can choose to convert
the files where you require strict typing and keep the other files without a
change.
So, it depends on you whether you wish to migrate all files from the beginning
of shift to typescript only for a project. It is all flexible for you.

Moving From JavaScript to TypeScript: Things Developers Should Know

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