npminstall

npm install?Node.js

?

1. npm?

npm?Node.js?Node.js

2. npm install?

`npm install`npm`node_modules``node_modules`?`package-lock.json`?`npm-shrinkwrap.json`

3. npm install?

`npm install`

a. ?`npm install`?`package.json`?

b. `npm install `?``?`npm install express`Express?

4.

`npm install``package.json`?npm`sudo npm install`?

npm install?Node.js