Encountering a 'Duplicate identifier' issue while trying to transition project to Typescript

Currently in the process of transitioning an existing JavaScript application to TypeScript. To facilitate a gradual conversion, I began by utilizing the "allowJs" compiler option to compile the original JavaScript code. However, as I start converting files to TypeScript, I encounter issues with namespace creation.

For instance, consider these two files: a new TypeScript file:

namespace myapp {
    export var c1 = 5;
}

And an old JavaScript file:

var myapp = myapp || {};
myapp.c2 = 4;

While this may result in valid JavaScript output, it triggers an error:

error TS2300: Duplicate identifier 'myapp'.

Is there a workaround to prevent this error or another method for converting files that share the same namespace?

Here is my tsconfig.json:

{
    "compilerOptions": {
        "allowJs": true,
        "outDir": "dist"
    }
}

Answer №1

To properly configure your tsconfig.json, make sure to specify either the "files" or "exclude" field to include or exclude files accordingly.

{
    "compilerOptions": {
        "allowJs": true,
        "outDir": "dist"
    },
    "files" : ["/path/to/ts/file.ts", ...]

}

OR

{
    "compilerOptions": {
        "allowJs": true,
        "outDir": "dist"
    },
    "exclude" : ["node_modules", "/path/to/build/js/"]

}

The issue arises because the TypeScript compiler is aware of both the original (TypeScript) source files and the compiled (JavaScript) files, leading to duplicate references. Your task is to either include only the source TypeScript files or exclude all non-TypeScript files.

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