Fixing "Property X does not exist on type Request" Error in TypeScript

Introduction

When working with TypeScript, you may occasionally encounter an error message like "Property X does not exist on type Request". This error typically arises when TypeScript cannot find a property within the Request object.

In this Byte, we'll explain the error and show how you can resolve it.

What does this error mean?

This usually occurs when TypeScript is unable to locate a property within the Request object, which is a part of the Express.js framework. This could happen for a few reasons, like the property being undefined, or TypeScript not being able to recognize the property. Here's an example of how the error might look:

app.get('/route', (req, res) => {
    console.log(req.fakeProperty);
});

In this case, TypeScript will throw an error saying Property 'fakeProperty' does not exist on type 'Request'.

Using --files Flag with ts-node

One way to fix this error is by using the --files flag with the ts-node command. This flag forces TypeScript to include all TypeScript files in the compilation, rather than just the ones that are directly imported or referenced.

$ ts-node --files server.ts

This command will compile all TypeScript files, which coudl include one that contains the missing property, thereby resolving the error.

Note: Using the --files flag will likely slow down the compilation process as it includes all TypeScript files in the compilation.

Adding Path to Types Directory in tsconfig.json

Another way to resolve this error is by adding the path to the types directory in your tsconfig.json file. This allows TypeScript to recognize the types and properties that are defined in your project.

{
    "compilerOptions": {
        "typeRoots": ["./node_modules/@types", "./types"]
    }
}

Here we've added the ./types directory to the typeRoots array, which inludes the object/property definition. Now, TypeScript will be able to recognize the properties defined in the types within this directory.

Conclusion

The "Property X does not exist on type Request" error in TypeScript is a common issue that shows up when TypeScript isn't able to locate a property within the Request object. By using the --files flag with the ts-node command or adding the path to the types directory in your tsconfig.json file, you can resolve this error.