Unable to load lsp backend for js-mode or js2-mode

[bobdobbs]

I've got the javascript layer running and have installed lsp-mode

In order to set up lsp-mode, I've been following the documention provided here:
https://develop.spacemacs.org/layers/+lang/javascript/README.html#backends

Following the documentation, I've added these lines to my spacemacs config.
(I've also tried removing them my spacemacs file and moving them to ~/.emacs.d/init.el. This gets the same results)

    ((js-mode (javascript-backend . lsp)))
   ((js2-mode (javascript-backend . lsp)))

Starting spacemacs with --debug-init yields this message:

Debugger entered--Lisp error: (invalid-function (js2-mode (javascript-backend . lsp)))

The full message is as follows

[lebensterben]

Please post your .spacemacs

[bobdobbs]

Please post your .spacemacs

https://gist.github.com/bobdobbs/a5cdf858293a6f72d65e235d3567cd9f

[lebensterben]

First,
Where in the documentation do you find it telling you to have

    ((js-mode (javascript-backend . lsp)))
   ((js2-mode (javascript-backend . lsp)))

They are not valid Lisp expressions.

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Second, all user configuration should not pass the last line of .spacemacs as can seen here.

[bobdobbs]

Where in the documentation do you find it telling you to have

This is under "2.5 Choosing a backend"

;;; Directory Local Variables
;;; For more information see (info "(emacs) Directory Variables")

((js2-mode (javascript-backend . lsp)))

[lebensterben]

In this very section

lsp backend will be automatically chosen if the layer lsp is used and you did not specify any value for javascript-backend

So you don't have to set anything if you want to use lsp as backend.

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As for the code you injected,

First there's no mentioning of js-mode. You should not invent it by yourself.
Second, just above the code example it says:

Backend can be chosen on a per project basis using directory local variables (files named .dir-locals.el at the root of a project)

So it clearly says they're used as directory local variable, which are set in .dir-locals.el at the root of a project, NOT in your .spacemacs.