Error installing plugin with message 'Error: Line 16: Unexpected token let'

I’ve read other issues and believe this error is similar but sufficiently different from other reported cases, including this one here: https://github.com/kazupon/vue-cli-plugin-i18n/issues/9,

Running vue add i18n fails to complete (the generator???) on a real project that I am building. If I generate just a blank project with minimal options as the default then the plugin installs OK; however, this isn’t my reality becuase I am working on a Production app. The real noteworthy differences I can discern between an empty project and mine, is that my real project has a few other components such as vuex, vuetify, and typescript and completed vue components – that I need to localize.

Hope you can help. package.txt

I’ve attached my package.json (as package.txt since package.json was blocked) in case it helps pinpoint the versions of other plugins I am using. I’d appreciate your input on what I am doing wrong or a fix.

My environment: OSX Mojave, Node 10.3.0, Error log:

$ vue add i18n

📦  Installing vue-cli-plugin-i18n...

+ vue-cli-plugin-i18n@0.5.1
added 5 packages from 3 contributors and audited 40202 packages in 15.011s
found 6 vulnerabilities (1 low, 4 high, 1 critical)
  run `npm audit fix` to fix them, or `npm audit` for details
✔  Successfully installed plugin: vue-cli-plugin-i18n

? The locale of project localization. en
? The fallback locale of project localization. en
? The directory where store localization messages of project. It's stored under `src` directory. locales
? Enable locale messages in Single file components ? No

🚀  Invoking generator for vue-cli-plugin-i18n...
 ERROR  Error: Line 16: Unexpected token let
Error: Line 16: Unexpected token let
    at ErrorHandler.constructError (/Users/calvinnguyen/.nvm/versions/node/v10.3.0/lib/node_modules/@vue/cli/node_modules/esprima/dist/esprima.js:5012:22)
    at ErrorHandler.createError (/Users/calvinnguyen/.nvm/versions/node/v10.3.0/lib/node_modules/@vue/cli/node_modules/esprima/dist/esprima.js:5028:27)
    at Parser.unexpectedTokenError (/Users/calvinnguyen/.nvm/versions/node/v10.3.0/lib/node_modules/@vue/cli/node_modules/esprima/dist/esprima.js:1985:39)
    at Parser.throwUnexpectedToken (/Users/calvinnguyen/.nvm/versions/node/v10.3.0/lib/node_modules/@vue/cli/node_modules/esprima/dist/esprima.js:1995:21)
    at Parser.consumeSemicolon (/Users/calvinnguyen/.nvm/versions/node/v10.3.0/lib/node_modules/@vue/cli/node_modules/esprima/dist/esprima.js:2297:23)
    at Parser.parseLabelledStatement (/Users/calvinnguyen/.nvm/versions/node/v10.3.0/lib/node_modules/@vue/cli/node_modules/esprima/dist/esprima.js:4029:19)
    at Parser.parseStatement (/Users/calvinnguyen/.nvm/versions/node/v10.3.0/lib/node_modules/@vue/cli/node_modules/esprima/dist/esprima.js:4122:97)
    at Parser.parseStatementListItem (/Users/calvinnguyen/.nvm/versions/node/v10.3.0/lib/node_modules/@vue/cli/node_modules/esprima/dist/esprima.js:3393:31)
    at Parser.parseScript (/Users/calvinnguyen/.nvm/versions/node/v10.3.0/lib/node_modules/@vue/cli/node_modules/esprima/dist/esprima.js:4723:29)
    at Object.parse (/Users/calvinnguyen/.nvm/versions/node/v10.3.0/lib/node_modules/@vue/cli/node_modules/esprima/dist/esprima.js:122:61)

[wolfmon]

It appears that during initialization the plugin will need to write to vue.config.js. This issue is likely caused by that config file not being empty. Try backup the existing content of vue.config.js and empty that file, if the initialization is successful you can put the original content back in. Hope this would help.

[bmdelacruz]

Hello! I also experienced this error. Here’s the console log:

📦  Installing vue-cli-plugin-i18n...

+ vue-cli-plugin-i18n@0.5.1
updated 1 package and audited 26257 packages in 41.819s
found 0 vulnerabilities

✔  Successfully installed plugin: vue-cli-plugin-i18n

? The locale of project localization. en
? The fallback locale of project localization. en
? The directory where store localization messages of project. It's stored under `src` direc
tory. locales
? Enable locale messages in Single file components ? No

🚀  Invoking generator for vue-cli-plugin-i18n...
 ERROR  Error: Line 32: Unexpected token <
Error: Line 32: Unexpected token <
    at ErrorHandler.constructError (/usr/local/lib/node_modules/@vue/cli/node_modules/esprima/dist/esprima.js:5012:22)
    at ErrorHandler.createError (/usr/local/lib/node_modules/@vue/cli/node_modules/esprima/dist/esprima.js:5028:27)
    at Parser.unexpectedTokenError (/usr/local/lib/node_modules/@vue/cli/node_modules/esprima/dist/esprima.js:1985:39)
    at Parser.throwUnexpectedToken (/usr/local/lib/node_modules/@vue/cli/node_modules/esprima/dist/esprima.js:1995:21)
    at Parser.parsePrimaryExpression (/usr/local/lib/node_modules/@vue/cli/node_modules/esprima/dist/esprima.js:2366:38)
    at Parser.inheritCoverGrammar (/usr/local/lib/node_modules/@vue/cli/node_modules/esprima/dist/esprima.js:2285:37)
    at Parser.parseLeftHandSideExpressionAllowCall (/usr/local/lib/node_modules/@vue/cli/node_modules/esprima/dist/esprima.js:2899:26)
    at Parser.inheritCoverGrammar (/usr/local/lib/node_modules/@vue/cli/node_modules/esprima/dist/esprima.js:2285:37)
    at Parser.parseUpdateExpression (/usr/local/lib/node_modules/@vue/cli/node_modules/esprima/dist/esprima.js:3004:26)
    at Parser.parseUnaryExpression (/usr/local/lib/node_modules/@vue/cli/node_modules/esprima/dist/esprima.js:3048:26)

I looked into the files that the plugin modifies and found out that my main.ts’s line 32 contains the code below. I temporarily commented it out, ran vue add i18n again, and then it worked.

(<any>window).mockController = mockController; // DEBUG

It fails because Esprima encountered a line on my main.ts file that contains Typescript specific code, i.e. type cast syntax.