Problem Summary
You’re managing a growing JavaScript project and things are getting messy – bugs are harder to catch, refactoring feels dangerous, and your team is spending more time debugging than building features. This is the classic sign that your project might have outgrown JavaScript’s flexibility and could benefit from TypeScript’s type safety and better tooling support.
Step-by-Step Fixes
Step 1: Audit Your Current JavaScript Codebase
Start by running a quick health check on your existing JavaScript project. Open your terminal and install a code complexity analyzer:
“`bash
npm install -g jscpd
jscpd src –min-lines 5 –min-tokens 50
“`
This will show you duplicate code patterns and complexity hotspots. If you’re seeing lots of duplication or files over 300 lines, that’s a yellow flag. Check your bug tracking system too – if more than 30% of your bugs are type-related errors (undefined properties, wrong function arguments), you’ve got a strong case for TypeScript.
Step 2: Try TypeScript on One Small Module First
Don’t panic and try to convert everything at once. Pick your smallest, most isolated module – maybe a utility file or a simple component. Rename it from `.js` to `.ts` and add TypeScript to your project:
“`bash
npm install –save-dev typescript @types/node
npx tsc –init
“`
In your `tsconfig.json`, set these beginner-friendly options:
“`json
{
“compilerOptions”: {
“allowJs”: true,
“checkJs”: false,
“strict”: false,
“noImplicitAny”: false
}
}
“`
This lets TypeScript and JavaScript coexist peacefully while you test the waters.
Step 3: Measure the Real Impact
After converting that first module, track these metrics for two weeks:
- Bug count in that module vs others
- Time spent debugging
- How confident developers feel making changes
Create a simple spreadsheet with columns for “Module Name”, “Bugs This Week”, “Hours Debugging”, and “Developer Confidence (1-10)”. Real data beats gut feelings every time.
Step 4: Set Clear Migration Triggers
Your project needs TypeScript when you hit any two of these thresholds:
- More than 5 developers touching the codebase regularly
- Over 50,000 lines of JavaScript code
- More than 10 npm packages as dependencies
- Customer-facing API with external developers
- Refactoring takes more than a day because you’re scared of breaking things
Step 5: Create a Gradual Migration Plan
If you decide to switch, here’s a battle-tested migration approach:
“`javascript
// Week 1-2: Configure TypeScript for mixed codebase
// tsconfig.json
{
“compilerOptions”: {
“allowJs”: true,
“target”: “ES2020”,
“module”: “commonjs”,
“outDir”: “./dist”
},
“include”: [“src/*/“],
“exclude”: [“node_modules”]
}
// Week 3-4: Convert shared utilities and types
// Week 5-8: Convert core business logic
// Week 9-12: Convert UI components
// Week 13+: Tighten TypeScript strictness gradually
“`
Step 6: Build Team Buy-In
Schedule a 30-minute team meeting. Show them this simple before/after example:
JavaScript (before):
“`javascript
function calculatePrice(items, discount) {
return items.reduce((total, item) => {
return total + item.price item.quantity;
}, 0) (1 – discount);
}
// Bug waiting to happen:
calculatePrice([{price: 10}], “20%”); // Runtime error!
“`
TypeScript (after):
“`typescript
interface Item {
price: number;
quantity: number;
}
function calculatePrice(items: Item[], discount: number): number {
return items.reduce((total, item) => {
return total + item.price item.quantity;
}, 0) (1 – discount);
}
// Error caught at compile time!
calculatePrice([{price: 10}], “20%”); // TypeScript error
“`
Likely Causes
Cause #1: Your Team is Burning Out on Runtime Errors
Check your error logs from the last month. If you see patterns like “Cannot read property ‘x’ of undefined” or “x is not a function” appearing more than 10 times weekly, your team is fighting problems TypeScript would prevent automatically.
Pull up your error tracking tool (Sentry, Rollbar, or even server logs) and search for these patterns. Count them. If it’s taking more than 2 hours per week to fix these preventable bugs, TypeScript will pay for itself in saved debugging time within the first month.
Cause #2: Onboarding New Developers Takes Forever
Time how long it takes a new developer to make their first meaningful code change. If it’s more than 3 days, you probably lack the self-documenting code that TypeScript provides through types.
Ask your newest team member: “What was the hardest part about understanding our codebase?” If they mention not knowing what functions expect or return, that’s TypeScript calling your name.
Cause #3: Refactoring Feels Like Defusing a Bomb
Open your version control system and look at the last 5 major refactoring pull requests. Count how many bugs were introduced despite code reviews. If it’s more than 2 bugs per refactoring, your JavaScript project has grown beyond what dynamic typing can safely handle.
Try this test: Pick a function used in more than 10 places and try to add a new required parameter. In JavaScript, you’ll need to manually check every single usage. In TypeScript, the compiler does this for you instantly.
When to Call a Technician
You should bring in a TypeScript consultant or experienced developer when:
- Your project has more than 100,000 lines of JavaScript code
- You’re dealing with complex generic types or need to integrate with multiple third-party TypeScript libraries
- Your team has tried migrating but keeps hitting mysterious compiler errors
- You need to maintain backward compatibility with a JavaScript SDK
Don’t feel bad about getting help – even teams at Microsoft and Google bring in TypeScript experts for large migrations. A week of expert guidance can save months of trial and error.
Copy-Paste Prompt for AI Help
Here’s a prompt you can paste into ChatGPT or Claude when you need specific migration help:
“`
I have a JavaScript project with [NUMBER] lines of code and [NUMBER] developers.
Main frameworks: [LIST YOUR FRAMEWORKS]
Main problems: [LIST YOUR SPECIFIC PAIN POINTS]
Should I migrate to TypeScript? If yes, create a specific 12-week migration plan for my situation, including:
- Which files/modules to convert first
- Specific tsconfig.json settings for my frameworks
- How to handle [SPECIFIC LIBRARY NAME] that doesn’t have TypeScript types
- Training resources for my team
- How to measure migration success
My biggest concern is: [YOUR MAIN WORRY]
“`
Remember, the question isn’t really “JavaScript or TypeScript?” anymore in 2025. It’s “When does my project need TypeScript’s safety net?” For most teams, that moment comes when fixing preventable bugs starts eating more time than building new features. Trust your instincts – if you’re reading this article, you’re probably already there.