I have tried :

$ sudo apt update

and

$ sudo apt install nodejs

But there is still the same error. I hope somebody can help me.:)

I hope someone is able to help me. If i type npm start the following error message appears:

pi@raspberrypi:~/MagicMirror $ npm start

> magicmirror@2.1.3 start /home/pi/MagicMirror
> sh run-start.sh

run-start.sh: 4: run-start.sh: electron: not found

npm ERR! magicmirror@2.1.3 start: `sh run-start.sh`
npm ERR! Exit status 127
npm ERR! 
npm ERR! Failed at the magicmirror@2.1.3 start script.
npm ERR! This is most likely a problem with the magicmirror package,
npm ERR! not with npm itself.
npm ERR! Tell the author that this fails on your system:
npm ERR!     sh run-start.sh
npm ERR! You can get their info via:
npm ERR!     npm owner ls magicmirror
npm ERR! There is likely additional logging output above.
npm ERR! System Linux 4.4.34-v7+
npm ERR! command "/usr/bin/nodejs" "/usr/bin/npm" "start"
npm ERR! cwd /home/pi/MagicMirror
npm ERR! node -v v0.10.29
npm ERR! npm -v 1.4.21
npm ERR! code ELIFECYCLE
npm WARN This failure might be due to the use of legacy binary "node"
npm WARN For further explanations, please read
/usr/share/doc/nodejs/README.Debian
 
npm ERR! 
npm ERR! Additional logging details can be found in:
npm ERR!     /home/pi/MagicMirror/npm-debug.log
npm ERR! not ok code 0
pi@raspberrypi:~/MagicMirror $