TypeScript 6.0: The migration release that demands your attention

TypeScript 6.0 isn't about flashy new features - it's about forcing your codebase to grow up. This release is a deliberate transition that strips away outdated defaults and deprecated patterns, preparing the ecosystem for TypeScript 7.0's complete rewrite in Go.

The key insight here isn't what TypeScript added, but what it's taking away - and why that matters for every TypeScript project in production.

The new defaults will break your assumptions

TypeScript 6.0 fundamentally shifts what "default" means. Where previous versions erred on the side of compatibility, 6.0 assumes you're working in a modern JavaScript environment:

• Default `target` is now `es2025` - TypeScript assumes your runtime supports cutting-edge JavaScript
• Default `module` is now `esnext` - ESM-first is no longer optional
• Stricter checking is the expected path - loose TypeScript is being phased out

This means projects that relied on TypeScript's previous conservative defaults will suddenly face build failures and type errors that weren't there before.

The deprecation list reveals TypeScript's future direction

More telling than the new features are the deprecations. Each deprecated option represents a pattern TypeScript wants to eliminate:

`moduleResolution: "node"` is deprecated in favor of nodenext or bundler. This isn't just a naming change - it's TypeScript acknowledging that the old Node.js resolution algorithm doesn't match how modern tooling actually works.

`baseUrl` is deprecated because path mapping through baseUrl was always a hack. The replacement is explicit paths configuration or proper package subpath imports:

1// Old approach (now deprecated)
2{
3  "baseUrl": "./src",
4  "paths": {
5    "*": ["*"]
6  }
7}
8
9// New approach
10{
11  "paths": {
12    "@/*": ["./src/*"],
13    "@/components/*": ["./src/components/*"]
14  }
15}

`outFile` is deprecated because bundlers have won the build tooling war. TypeScript is admitting that trying to be a bundler was a mistake.

These aren't arbitrary changes - they're TypeScript admitting where its original design assumptions were wrong.

Why this migration matters more than others

Typical TypeScript releases add features you can adopt gradually. TypeScript 6.0 is different because it changes the baseline. Projects that don't migrate aren't just missing out on new features - they're accumulating technical debt that will become a crisis when TypeScript 7.0 drops legacy support entirely.

The ignoreDeprecations flag exists as a temporary escape hatch:

1{
2  "compilerOptions": {
3    "ignoreDeprecations": "6.0"
4  }
5}

But this is explicitly designed as a short-term bridge, not a permanent solution. When TypeScript 7.0 arrives with its Go-based compiler, deprecated features will simply disappear.

The practical migration path

The safest approach is to make your configuration explicit rather than relying on defaults:

1{
2  "compilerOptions": {
3    // Be explicit about your target environment
4    "target": "es2022", // or whatever your runtime actually supports
5    "module": "esnext",
6    
7    // Choose the right resolution strategy
8    "moduleResolution": "bundler", // for Vite, Webpack, etc.

The key is auditing your current tsconfig.json against the deprecation list and making conscious choices about each setting.

Import attributes: a syntax migration you can't avoid

One breaking change affects syntax directly. Import assertions using assert are being replaced with with:

1// Old syntax (being phased out)
2import data from './data.json' assert { type: 'json' };
3
4// New syntax
5import data from './data.json' with { type: 'json' };

This isn't just TypeScript - it's following the JavaScript specification. But it means existing code will need updates.

Why this matters

TypeScript 6.0 represents a philosophical shift. The TypeScript team is using this release to clean house before the major architectural changes in 7.0. Projects that treat this as "just another update" will face a much more painful migration later.

The broader message is that TypeScript is maturing from a tool that accommodated legacy JavaScript patterns to one that enforces modern best practices. That's ultimately good for code quality and developer experience, but it requires active participation in the migration.

Your action plan: Audit your tsconfig.json against the deprecation warnings, run your build with TypeScript 6.0 in a branch, and fix the issues now while you can use ignoreDeprecations as a fallback. Waiting until TypeScript 7.0 removes that safety net entirely is a risk most production codebases can't afford to take.