TS1413: File is output from referenced project specified here

TypeScript is a superset of JavaScript that brings optional static typing and other powerful tools to make JavaScript development more robust and scalable. Static typing allows you to define the structure of variables, functions, objects, and beyond, ensuring that your code adheres to strict rules before it even runs. This feature eliminates many common runtime errors by catching issues during the development process. If you're just starting with TypeScript—or want to gain deeper insights into advanced topics like type definitions, interfaces, and enums—subscribe to our blog and consider using AI-powered tools like gpteach.us to enhance your programming skills.

In this article, we are going to shed light on a common TypeScript error: TS1413: File is output from referenced project specified here. Before we dive into the main topic, let's briefly cover an essential foundational concept: what types are.

What Are Types in TypeScript?

Types are the core building blocks in TypeScript. Simply put, a type describes the shape or kind of value a variable can hold. This ensures that operations performed on the variable are valid. For example:

let age: number = 25; // `age` is expected to hold a number
age = "twenty-five";  // ERROR: Type 'string' is not assignable to type 'number'

Why Types Matter

Using types in your code promotes better readability, safer refactoring, and fewer bugs. Types can enforce stricter rules while working with data structures like arrays, objects, and functions, aiding developers during development. For instance:

function greet(name: string): string {
  return `Hello, ${name}!`;
}

greet("Alice");    // Valid
greet(42);         // ERROR: Argument of type 'number' is not assignable to type 'string'

Now that we’ve understood the basics of types, let’s focus on TS1413: File is output from referenced project specified here.

Understanding the Error: TS1413: File is output from referenced project specified here

What Is This Error?

The TS1413: File is output from referenced project specified here. error arises when TypeScript gets confused about how files in a project are interconnected due to improper configuration in your project’s tsconfig.json. This error often happens when you're working with multi-project repositories (monorepos) or TypeScript’s project references. Essentially, TypeScript is saying: "This file is already output by a referenced project, and you shouldn’t modify or use it directly."

To explain this in plain terms: TypeScript supports breaking a project into smaller, reusable modules using project references (a way to link multiple tsconfig.json files together). If files overlap or improperly reference one another, you’ll encounter the TS1413 error.

Common Scenario That Causes This Error

Suppose you have two TypeScript projects: ProjectA and ProjectB, where ProjectB depends on ProjectA. When you set up the tsconfig.json for ProjectB, you might accidentally include an output file from ProjectA. Output files are files that have been compiled into JavaScript by tsc (TypeScript Compiler).

Example Code for Error

Let’s demonstrate with an incorrect setup:

ProjectA/tsconfig.json

{
  "compilerOptions": {
    "composite": true,    // Enables project references
    "outDir": "./dist"    // Output directory for compiled files
  },
  "include": ["src"]
}

ProjectB/tsconfig.json

{
  "compilerOptions": {
    "composite": true,
    "outDir": "./dist"
  },
  "references": [
    { "path": "../ProjectA" }
  ],
  "include": ["src", "../ProjectA/dist"] // Incorrect: Including output files from ProjectA
}

Here, ProjectB is trying to reference the dist directory (compiled output) of ProjectA, which is unnecessary because TypeScript already knows how to reference the source files from ProjectA via the references field.

How To Fix TS1413: File is output from referenced project specified here

To resolve the error, follow these steps:

  1. Do Not Directly Include Compiled Output
    • Avoid listing the outDir or compiled files of a referenced project in the include or files array.
    • Instead, let project references manage dependencies.

Corrected ProjectB/tsconfig.json:

{
     "compilerOptions": {
       "composite": true,
       "outDir": "./dist"
     },
     "references": [
       { "path": "../ProjectA" }
     ],
     "include": ["src"], // Only include your source files
   }

  1. Check TypeScript Version

    • Ensure you’re using a version of TypeScript that supports project references (TypeScript 3.0 or newer).

  2. Clean Your Output Directories

    • After making changes, delete the dist directories and rebuild your projects to ensure the compiled files do not conflict.

Run the following commands:

rm -rf ./ProjectA/dist ./ProjectB/dist
   tsc -b ./ProjectA ./ProjectB
  1. Understand the Composite Setting
    • If you're including files, make sure those files are source files—not output files—generated by the compiler.

Important to Know!

  1. What Are Project References?

    • Project references are a way to structure large codebases. They allow you to divide your code into independent pieces, each with its own tsconfig.json, while maintaining type safety across projects.

  2. What is composite in tsconfig?

    • Setting "composite": true in tsconfig.json tells TypeScript that your project can be used as a dependency of another project.

  3. Why Should You Not Reference Output Files?

    • Referencing compiled files defeats the purpose of TypeScript’s strong typing as it bypasses type checking on the source files.

Frequently Asked Questions (FAQ)

Q: What triggers TS1413 in most setups?

A: This error typically occurs when you include compiled files (e.g., dist or build folders) in a project that references another project, causing conflicts in the type-resolution process.

Q: Can I fix this by tweaking tsconfig.json?

A: Yes! Ensure that your tsconfig.json excludes output directories and relies on project references for inter-project dependencies.

Q: Is this error specific to large projects?

A: Not necessarily. Even a small project with misconfigured tsconfig.json can trigger TS1413.

Final Thoughts

The TS1413: File is output from referenced project specified here. error can be daunting for developers unfamiliar with TypeScript’s project references. However, by understanding how to properly configure the tsconfig.json file and avoid referencing compiled output, you can resolve the issue quickly. If you’re working with large TypeScript projects, take a moment to review the fundamentals of type declarations, project references, and configuration best practices to avoid running into similar issues. Happy coding!