Error: The mysterious absence of __assign - a headache for NativeScript Object Spread

Everything was going smoothly with my native-script project until I encountered this issue:

JS: EXCEPTION: Uncaught (in promise): ReferenceError: __assign is not defined

The error originates from this line of code:

return [...state, { ...action.payload, success: false }];

Take a look at my tsconfig.json:

{
    "compilerOptions": {
        "module": "commonjs",
        "target": "es5",
        "experimentalDecorators": true,
        "emitDecoratorMetadata": true,
        "noEmitHelpers": true,
        "noEmitOnError": true
    },
    "exclude": [
        "node_modules",
        "platforms",
        "**/*.aot.ts"
    ]
}

It seems that Typescript is not including the helper function __assign in the compiled source, which is necessary for implementing object spread syntax. Any insights on why this might be happening?

typescriptnativescriptspread-syntax

Answer №1

I am thrilled to share that I have discovered the solution to this issue. Take a look at this GitHub repository for a detailed explanation, but here's a brief summary:

The presence of the flag noEmitHelpers in tsconfig.json instructs Typescript to exclude these 'helpers' (like __assign) in any file that requires them.

{
  "compilerOptions": {
    // setting this to false resolves the issue, but it duplicates helpers in each file
    "noEmitHelpers": false
  }
}

In the latest version of Typescript, there is a more efficient method to handle this using the flag importHelpers (refer to the compiler options):

{
  "compilerOptions": {
    "noEmitHelpers": true,
    "importHelpers": true // preferred approach
  }
}

This update will enable object spread functionality and prevent code duplication across files.

You may also need to execute npm install tslib --save to eliminate IDE errors.

Answer №2

Did you consider including "lib": "es6" in your tsconfig file?

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