External node modules written in TypeScript can occasionally be transpiled into both `module.exports` and `

Question

External node modules written in TypeScript can occasionally be transpiled into both `module.exports` and `

Currently, I am in the process of transforming my node application to utilize TypeScript external modules. While everything runs smoothly when executing the app, I encountered an issue with my mocha tests "exploding" after converting some of my .ts files due to a

SyntaxError: Unexpected reserved word

.

After extensive troubleshooting, I discovered a reproducible failure scenario. I have a straightforward autoRoles.ts file that defines the user roles available. Before implementing external modules, it appeared as follows:

/// <reference path="../../typings/backend_typings.d.ts" />

module.exports.roles = {
  // role definitions
}

Now, post-conversion:

/// <reference path="../../typings/backend_typings.d.ts" />

export let roles = {
  // role definitions
}

Upon running the mocha tests, the following error is generated:

>> Mocha exploded!
>> SyntaxError: Unexpected reserved word
... (additional error details)

I can switch between the old and new implementations for the autoRoles.ts file resulting in mocha passing or failing, respectively. Line 77 of userRoles.ts contains a require('<path>/autoRoles').

When comparing the transpiled versions, the only discrepancy lies in the usage of 'module.exports' in the old version and just 'exports' in the new one.

Old:

/// <reference path="../../typings/backend_typings.d.ts" />
exports.roles = {
  // role definitions
}

New:

/// <reference path="../../typings/backend_typings.d.ts" />
module.exports.roles = {
  // role definitions
}

Despite being aware that "exports" is simply a shorthand for "module.exports", the reason behind this causing mocha failures eludes me. It's puzzling why merely switching between the two versions without any other alterations leads to mocha "exploding." Additionally, I've observed that tsc occasionally uses "module.exports" while other times opting for "exports" in transpiled modules. The inconsistency raises questions - why are these discrepancies present and more importantly, what triggers mocha to explode?

node.js typescript commonjs

Answer 1

Answer №1

Encountered unexpected reserved word

To resolve this issue, make sure to include "use strict"; at the beginning of your file. It is possible that you are using a variable name that is a reserved keyword. For more information on strict mode and avoiding reserved keywords, refer to this documentation. TypeScript will also provide warnings for such variable names if the strict mode header is present in the file.

The error is not related to module.exports.roles = {...}.

I have observed that transpiled modules may sometimes use "module.exports" and other times use "exports".

This behavior is consistent with the nodejs convention, optimizing for parsing efficiency by reducing the number of characters (bytes) needed at runtime.

export let foo = 123;

Translates to

exports.foo = 123;

(since exports == module.export, therefore exports.foo == module.export.foo ... as you already know). However, in the case of:

let foo = 123;
export = foo;

It results in

var foo = 123;
module.exports = foo;

Because reassigning exports with exports = foo would mean module.export !== exports. Therefore, exports should be used for extension purposes only, not for assignment.

Answer 2

Encountered unexpected reserved word

To resolve this issue, make sure to include "use strict"; at the beginning of your file. It is possible that you are using a variable name that is a reserved keyword. For more information on strict mode and avoiding reserved keywords, refer to this documentation. TypeScript will also provide warnings for such variable names if the strict mode header is present in the file.

The error is not related to module.exports.roles = {...}.

I have observed that transpiled modules may sometimes use "module.exports" and other times use "exports".

This behavior is consistent with the nodejs convention, optimizing for parsing efficiency by reducing the number of characters (bytes) needed at runtime.

export let foo = 123;

Translates to

exports.foo = 123;

(since exports == module.export, therefore exports.foo == module.export.foo ... as you already know). However, in the case of:

let foo = 123;
export = foo;

It results in

var foo = 123;
module.exports = foo;

Because reassigning exports with exports = foo would mean module.export !== exports. Therefore, exports should be used for extension purposes only, not for assignment.

Answer 3

Answer №2

After extensive debugging, I discovered that mocha was not utilizing the transpiled .js source code files generated by tsc. It seemed to be attempting to execute the "export var roles" function from the .ts file, where 'export' is a reserved word.

I stumbled upon this informative post, which hinted at mocha performing its own transpiling. The suggestion was to use "typescript-require", but it seems that this package is in the process of being replaced by "ts-node". As a result, I updated my grunt-ts configuration as follows:

mochaTest: {
    test: {
        options: {
            reporter: 'spec',
            require: [
                'ts-node/register'
            ]
        },
        src: ['lib/test/**/*.spec.js']
    }
},

This solution worked well for me, though I would appreciate any insights into what exactly mocha was doing behind the scenes. Furthermore, I am curious as to why mocha was able to handle transpiling and did not detect the "reserved word" issue in other .ts files using export statements.

Edit 10/30/2015:

I eventually realized why mocha was attempting to run my .ts files. I had mistakenly imported some of them with require('/path/file.ts') instead of omitting the '.ts' extension. Consequently, I no longer required 'ts-node' in my mocha runner. This oversight also clarified why mocha was only causing errors in certain .ts files.

Answer 4

After extensive debugging, I discovered that mocha was not utilizing the transpiled .js source code files generated by tsc. It seemed to be attempting to execute the "export var roles" function from the .ts file, where 'export' is a reserved word.

I stumbled upon this informative post, which hinted at mocha performing its own transpiling. The suggestion was to use "typescript-require", but it seems that this package is in the process of being replaced by "ts-node". As a result, I updated my grunt-ts configuration as follows:

mochaTest: {
    test: {
        options: {
            reporter: 'spec',
            require: [
                'ts-node/register'
            ]
        },
        src: ['lib/test/**/*.spec.js']
    }
},

This solution worked well for me, though I would appreciate any insights into what exactly mocha was doing behind the scenes. Furthermore, I am curious as to why mocha was able to handle transpiling and did not detect the "reserved word" issue in other .ts files using export statements.

Edit 10/30/2015:

I eventually realized why mocha was attempting to run my .ts files. I had mistakenly imported some of them with require('/path/file.ts') instead of omitting the '.ts' extension. Consequently, I no longer required 'ts-node' in my mocha runner. This oversight also clarified why mocha was only causing errors in certain .ts files.

External node modules written in TypeScript can occasionally be transpiled into both `module.exports` and `

Answer №1

Answer №2

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