Visual Studio Task Runner Error with ES6

Question

I am running Visual Studio 2017 and use the Task Runner to run tasks in my gulpfile. I recently updated a gulp task to ES6 and now am getting this error:

Failed to run "C:\Users\nz9rcn\Code\WebUI\Gulpfile.js"... cmd.exe /c gulp --tasks-simple C:\Users\nz9rcn\Code\WebUI\gulp-tasks\lesslint.js:5 let fail = false; ^^^ SyntaxError: Block-scoped declarations (let, const, function, class) not yet supported outside strict mode at exports.runInThisContext (vm.js:53:16) at Module._compile (module.js:373:25) at Object.Module._extensions..js (module.js:404:10) at Module.load (module.js:343:32) at Function.Module._load (module.js:300:12) at Module.require (module.js:353:17) at require (internal/module.js:12:17) at task (C:\Users\nz9rcn\Code\WebUI\gulpfile.js:24:25) at Object.<anonymous> (C:\Users\nz9rcn\Code\WebUI\gulpfile.js:37:23) at Module._compile (module.js:397:26)

Can't find a place to adjust the settings causing this error (strict mode). Please help. Thanks

Surovy

Are you sure Visual Studio supports ES6 out of the box? By the error it looks like it doesn't recognize ES6 syntax - maybe you need a tool like Babel to transpire first? Not sure how that would be accomplished with this task runner though. – Vardhamana

@Vardhamana according to this document, ES6 is supported: learn.microsoft.com/en-us/scripting/javascript/… – Surovy

Strict mode is a language feature that's enabled within code. Include "use strict"; either as the 1st line of the file or 1st line of the function's body that's using let. – Licking

@JonathanLonowski I believe the issue is that Visual Studio is choosing to run code in 'use strict' mode, as I do not have the statement in my code, and therefore needs to be turned off in VS. I can't remove it from my code because it is not there. – Surovy

@BenRondeau It should be the other way. To use let, you'll have to use strict mode. Since you haven't opted into the mode, the declaration isn't permitted. (Though, that was a temporary restriction in Google's V8. The version in Node 8 should allow let both with and without strict mode.) – Licking

@JonathanLonowski Problem solved below. Visual Studio was targeting an old version of Node to run ES6 – Surovy

Answer 1

Issue solved by un-checking the box for the Node.js binary used by Task Runner:

In the menu, go to Tools > Options > Projects and Solutions > Web Package Management > External Web Tools and DESELECT the option for $(VSINSTALLDIR)\Web\External

The version installed in that directory doesn't support ES6 apparently.

References for solution here and here.

Surovy

Thank you SOOOOO much for this ! – Swayder

I wish i could upvote this more than once. Thank you. – Eradicate