TypeScript 6.0 Migration Practical Guide: What Settings Your Team Needs to Fix Now Compared to the 7.0 Go Compiler

1. Problem definition

With TypeScript 6.0 officially released on March 17, 2026, build failures are occurring one after another in existing projects. The key causes are strict mode enabled by default, ES modules(esnext) default resolution, es2025 target default, etc. This is because the settings have been changed.

Problem this article solves:

• Team tsc build suddenly fails after upgrading to TypeScript 6.0
• Projects that need to maintain ES5/CommonJS/AMD legacy codebase
• Technology leaders needing a migration roadmap for TypeScript 7.0 (Go compiler)

Scope of application: Node.js 18+ environment, monorepo/multipackage structure, projects using modern frameworks such as Next.js/React/Nest.js

Scope of application: IE11 support project requiring ES5 target (separate transpiler required), Deno/Bun only project

2. Evidence and Comparison

The key changes in TypeScript 6.0 compared to the 5.x version are as follows:

Settings	TS 5.x default	TS 6.0 default	Migration Impact
strict	false	true	High - implicit any error spike
module	commonjs	esnext	High - require() syntax error
moduleResolution	node (node10)	nodenext/bundler	Medium - Change path resolution
target	es5/es2015	es2025	Low - targets modern browsers
noUncheckedSideEffectImports	false	true	Medium - polyfill import needs to be checked

Comparison of migration approaches:

Approach	Advantages	Disadvantage	Recommendation status
Gradual Migration	Spreading risk, easing team learning curve	Intermediate state management complex	Large-scale legacy project
Batch conversion (Big Bang)	Clean transitions, no intermediate states	Requires fixing many errors at once	Small project, codebase with high test coverage
Use ignoreDeprecations	Enable TS 6.0 immediately, with incremental fixes	Forced migration from TS 7.0	Not enough time, team can afford to reach TS 7.0

3. Step-by-step execution method

Step 1: Pre-test with RC version (1-2 hours)

#Test on a separate branch
git checkout -b ts6-migration
npm install -D typescript@rc

#build test
npx tsc --noEmit 2>&1 | tee ts6-errors.log

#Counts by Error Type
grep -oP "error TS\d+" ts6-errors.log | sort | uniq -c | sort -rn | head -20

Step 2: Add tsconfig.json compatible settings

{
  "compilerOptions": {
    //Explicit settings to maintain existing behavior
    "strict": false,                    //Progressive activation recommended
    "module": "commonjs",               //or "nodenext" for ESM
    "moduleResolution": "nodenext",     //node10 removed
    "target": "es2022",                 //Maintain lower versions when necessary
    "noUncheckedSideEffectImports": false,
    
    //Ignore deprecation warning (valid only until TS 7.0)
    "ignoreDeprecations": "6.0",
    
    //@types explicitly specified (auto-inclusion removed)
    "types": ["node", "jest"]
  }
}

Step 3: Import Assertions → Convert Import Attributes

//❌ Error in 6.0
import data from './config.json' assert { type: 'json' };

//✅ Correct grammar
import data from './config.json' with { type: 'json' };

Batch conversion command:

#Batch conversion with sed
find src -name "*.ts" -exec sed -i 's/assert {/with {/g' {} +

Step 4: Gradually enable strict mode

{
  "compilerOptions": {
    "strict": false,
    //Incremental activation with individual flags
    "noImplicitAny": true,           //Step 1
    "strictNullChecks": true,        //Step 2
    "strictFunctionTypes": true,     //Step 3
    "strictBindCallApply": true,     //Step 4
    "strictPropertyInitialization": true, //Step 5
    "noImplicitThis": true,          //Step 6
    "alwaysStrict": true             //Step 7 → strict: true conversion
  }
}

Step 5: Update dependencies

#@types/node update required
npm install -D @types/node@latest

#eslint-typescript plugin
npm install -D @typescript-eslint/parser@latest @typescript-eslint/eslint-plugin@latest

#Compatibility Verification
npm ls typescript @types/node

Step 6: Update CI/CD pipeline

# .github/workflows/ci.yml
jobs:
  build:
    strategy:
      matrix:
        typescript: ['5.8', '6.0']  #parallel testing
    steps:
      - run: npm install -D typescript@${{ matrix.typescript }}
      - run: npm run typecheck
      - run: npm run build

4. Pitfalls

Trap 1: moduleResolution: remove node

Symptoms: error TS2834: Relative import paths need explicit file extensions

Cause: moduleResolution: "node" (or "node10") option completely removed

Solution:

// tsconfig.json
{
  "compilerOptions": {
    "moduleResolution": "nodenext"  //or "bundler"
  }
}

//If it is an ESM project, specify the extension
import { util } from './utils.js';  //.js extension required

Trap 2: @types auto-include removal

Symptoms: Cannot find name 'process', Cannot find name 'Buffer'

Cause: node_modules/@types Auto-include is disabled

Solution:

{
  "compilerOptions": {
    "types": ["node", "jest", "webpack-env"]  //explicit declaration
  }
}

Trap 3: namespace → module keyword error

Symptoms: error TS1194: Export declarations are not permitted in a namespace

Cause: Legacy module MyLib { } grammar forced to namespace

Solution:

//❌ Legacy (Error)
module MyLib {
  export function hello() {}
}

//✅ Correct grammar
namespace MyLib {
  export function hello() {}
}

Trap 4: downlevelIteration flag error

Symptoms: error TS5107: Option 'downlevelIteration' has no effect

Cause: target: es2025 Flags that became unnecessary from the default value

Solution:Remove that option from tsconfig.json

Pit 5: Slow build speed due to stableTypeOrdering

Symptom:Type check speed slowed by 25%

Cause: When using --stableTypeOrdering flag for TS 7.0 compatibility

Solution: Disable in development environment, enable only in CI

# package.json
{
  "scripts": {
    "typecheck": "tsc --noEmit",
    "typecheck:strict": "tsc --noEmit --stableTypeOrdering"
  }
}

5. Action Checklist

Required confirmation items before distribution:

• ☐ npx tsc --noEmit Check 0 errors
• ☐ moduleResolution is set to nodenext or bundler
• ☐ types @types package required for array specified
• ☐ Import assertions converted to import attributes (assert → with)
If
• ☐ strict: false, individual strict flag gradual activation plan is established
• ☐ TS 5.8 + 6.0 parallel testing configured in CI pipeline
TS 7.0 migration schedule secured when using
• ☐ ignoreDeprecations: "6.0"

Definition of Done: npm run build passes with 0 warnings/errors in TS 6.0, and all tests succeed as before.

6. References

• TypeScript 6.0 RC official announcement - Microsoft DevBlogs (March 2026)
• TypeScript 6.0 Beta release and major changes - InfoQ (February 2026)
• TypeScript 6.0 RC Migration Guide - ReactLibraries (March 2026)
• TS 6.0.1 How to install RC build without breaking it - NTCompatible (March 2026)
• TypeScript 7.0 Go Compiler Unofficial Build - GitHub (2026)

7. Author Viewpoint

Recommendation: For most teams, gradual migration + ignoreDeprecations: "6.0" parallel is recommended. The reasons are as follows:

• TS 7.0 (Go compiler) is scheduled to be released in the summer of 2026, so there is no need to unreasonably remove all deprecated options in 6.0
Enabling
• strict: true at once can cause thousands of errors in large projects. Step-by-step application with individual flags is realistic
• Parallel testing of TS 5.8 and 6.0 in CI can detect compatibility issues early

Not recommended:

• Projects where maintaining ES5 targets is essential: Must stay at 5.8 instead of TS 6.0. An alternative is to convert ES5 with a separate transpiler (Babel/SWC) and then perform only the type check with TS 6.0
• TS 7.0 Direct: If you have time, you can also skip 6.0 and wait for 7.0 (Go compiler, 10x speed). However, since ignoreDeprecations will be removed in 7.0, advance preparation is essential

Conclusion: TypeScript 6.0 is cleanup release for the Go compiler transition in 7.0. There is no need to switch now, but if you create a clean codebase that does not depend on ignoreDeprecations, you can immediately benefit from the 10x faster build speeds in 7.0.