i want to install nodejs in ubuntu, I installed nodejs and checked its version, it works correctly but npm is not getting installed properly - ubuntu-16.04

Question

i have installed nodejs using the command :
curl -sL https://deb.nodesource.com/setup_7.x | sudo -E bash -
sudo apt-get install -y nodejs
after that i have checked its version and it shows :
v7.10.1
but when i checked the npm version using npm -v, it shows error
/usr/local/lib/node_modules/npm/node_modules/npm-package-arg/npa.js:6
let url
^^^
SyntaxError: Unexpected strict mode reserved word
at Module._compile (module.js:437:25)
at Object.Module._extensions..js (module.js:467:10)
at Module.load (module.js:356:32)
at Function.Module._load (module.js:312:12)
at Module.require (module.js:362:17)
at require (module.js:378:17)
at Object.<anonymous>
(/usr/local/lib/node_modules/npm/node_modules/npm-registry-
client/lib/access.js:5:11)
at Module._compile (module.js:449:26)
at Object.Module._extensions..js (module.js:467:10)
at Module.load (module.js:356:32)
for installing npm i have used command : sudo apt-get install npm, the it shows like this
sudo apt-get install npm
Reading package lists... Done
Building dependency tree
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:
The following packages have unmet dependencies:
npm : Depends: nodejs but it is not going to be installed
Depends: node-abbrev (>= 1.0.4) but it is not going to be installed
Depends: node-ansi (>= 0.3.0-2) but it is not going to be installed
Depends: node-ansi-color-table but it is not going to be installed
Depends: node-archy but it is not going to be installed
Depends: node-block-stream but it is not going to be installed
Depends: node-fstream (>= 0.1.22) but it is not going to be installed
Depends: node-fstream-ignore but it is not going to be installed
Depends: node-github-url-from-git but it is not going to be installed
Depends: node-glob (>= 3.1.21) but it is not going to be installed
Depends: node-graceful-fs (>= 2.0.0) but it is not going to be installed
Depends: node-inherits but it is not going to be installed
Depends: node-ini (>= 1.1.0) but it is not going to be installed
Depends: node-lockfile but it is not going to be installed
Depends: node-lru-cache (>= 2.3.0) but it is not going to be installed
Depends: node-minimatch (>= 0.2.11) but it is not going to be installed
Depends: node-mkdirp (>= 0.3.3) but it is not going to be installed
Depends: node-gyp (>= 0.10.9) but it is not going to be installed
Depends: node-nopt (>= 3.0.1) but it is not going to be installed
Depends: node-npmlog but it is not going to be installed
Depends: node-once but it is not going to be installed
Depends: node-osenv but it is not going to be installed
Depends: node-read but it is not going to be installed
Depends: node-read-package-json (>= 1.1.0) but it is not going to be installed
Depends: node-request (>= 2.25.0) but it is not going to be installed
Depends: node-retry but it is not going to be installed
Depends: node-rimraf (>= 2.2.2) but it is not going to be installed
Depends: node-semver (>= 2.1.0) but it is not going to be installed
Depends: node-sha but it is not going to be installed
Depends: node-slide but it is not going to be installed
Depends: node-tar (>= 0.1.18) but it is not going to be installed
Depends: node-underscore but it is not going to be installed
Depends: node-which but it is not going to be installed
E: Unable to correct problems, you have held broken packages.

Answer 1

Try this
update apt-get update
get install script and pass it to execute:
curl -sL https://deb.nodesource.com/setup_7.x | bash
and install node apt-get install nodejs
confirm that it was successful node -v npm installs automatically npm -v
Note - don't use apt-get install -y nodejs instead use apt-get install nodejs which will install specified node version and npm automatically.
I hope this will resolve your problem. I have done the above steps and updated successfully without any issues. If you have any issues or doubts let me know.

Answer 2

When you try to install a package what depends of other packages with apt-get, apt-get only tries to install the most important package, apt-get do not install the dependencies. So, there is another package manager like apt-get, called aptitude, what installs package and the dependencies. So you may do something like this:
sudo aptitude install npm