Upgrade the version of nodejs to 5.12.0 - node.js

Question

I tried to install node.js by NVM in Ubuntu 16.04 server by following this link. And I got:
root#instance-15s8fbzx:/opt# nodejs --version
v4.2.6
root#instance-15s8fbzx:/opt# npm --version
5.3.0
root#instance-15s8fbzx:/opt# node --version
v8.4.0
Then, we I run a mean-stack project by sudo npm start, I got
class User {
^^^^^
SyntaxError: Block-scoped declarations (let, const, function, class) not yet supported outside strict mode
Then, I saw this link, I think maybe because the nodejs version is not correct. I have another server with v5.12.0 as the version of nodejs, and the project worked well there.
Then, I tried to do
sudo npm install -g npm
sudo npm install -g n
sudo n stable
sudo ln -sf /usr/local/n/versions/node/8.4.0/bin/node /usr/bin/node
But the version of the nodejs is still 4.2.6. Does anyone know how to upgrade its version to 5.12.0?

Answer 1

After you have installed NVM and you have installed the necessary version of node, you select the node version as follows:
> nvm use v5.12.0

Answer 2

After upgrading to the Nodejs version, the following error occurred for the Laravel and VUE js packages I already had:
PHP Fatal error: During inheritance of IteratorAggregate: Uncaught
ErrorException: Return type of
Symfony\Component\HttpFoundation\ParameterBag::getIterator() should
either be compatible with IteratorAggregate::getIterator():
Traversable, or the #[\ReturnTypeWillChange] attribute should be used
to temporarily suppress the notice in
C:\xampp\htdocs\clerk\vendor\symfony\http-foundation\ParameterBag.php:210
To solve the issue, I did the following:
composer update
npm update
npm run dev
php artisan serve