TypeError: Cannot read property 'length' of undefined (Caused by arrow functions in module)

[PaddeK]

If i use arrow functions in a module i get an error while uploading the code via send button from WebIDE to espruino (wifi).

The error is:
TypeError: Cannot read property 'length' of undefined

Minimal test module (test.js):

'use strict';

let Test;

Test = function () {
    this.mtFn = () => {};
};
module.exports = Test;

Simply require the module and upload code to espruino will trigger the error.

Right hand side of WebIDE:

let Test = require('test');

If i replace the arrow function this.mtFn with a 'normal' function this.mtFn = function () {}; i get no error.

[gfwilliams]

Where does this error come from? The Web IDE? I guess it's not from Espruino itself as there is no use of .length in the code

Unfortunately Espruino doesn't support all of ES6 so let won't work correctly, but that shouldn't actually be your problem.

[PaddeK]

Yes it comes from the Web IDE and as far as i can tell the uploaded code works fine so far.

[gfwilliams]

Looks like it's a bug inside the esprima minification library that's being used.

If you turn off module minification in settings, or turn it to the online minification, it should work

[PaddeK]

Both suggestions work. I will use the online closure minifier for now.
Thank you!

[gfwilliams]

Closing this - as moved to EspruinoTools now: espruino/EspruinoTools#58