ExpressJS installation methods - node.js

Question

Firstly, I understand that since version 4 (express), the boilerplate HTML generator has been splintered off. However, does executing the command...
npm install -g express-generator
... and not...
npm install -g express
... automatically install the core express engine as well? I am asking this because, surprisingly, I was only instructed to install the first.
Secondly, an online tutorial instructs something similar to the following...
npm install -g express-generator
express --ejs pineapple-news
cd pineapple-news
npm install
However, on the contrary, I found that the official express documentation recommended this instead...
mkdir pineapple-news
cd pineapple-news
npm init
... hitting return for all the defaults and then ending with...
npm install express --save
As a newbie, I need to understand the differences between the two approaches and the reason for the differences. Any pointers would be highly appreciated.

Answer 1

Let me explain the two cases.
First case :
npm install -g express-generator
express --ejs pineapple-news
cd pineapple-news
npm install
Here, with the first line, you're installing express-generator globally. That is, after installing it globally, you can use it like any other program that can be invoked from the terminal. In the second line, you are invoking the express generator and specifying ejs as the template engine and pineapple-news as the project name. So, the express generator creates a folder named pineapple-express with the necessary sub folders, a default app.js file and a default package.json file. The package.json file thus created will have all the dependecies including express and ejs, the template engine to be used listed in it. Then, when you execute npm intall ,all the dependencies will be installed automatically.
Second case:
mkdir pineapple-news
cd pineapple-news
npm init
With the first and second line, you're creating a folder with the name as pineapple-express and entering inside it. The npm init command creates the package.json file after prompting you to specify some parameters such as project name, version, repository etc. The package.json file thus created will not have any dependencies listed in it. When you do npm install express --save, it will add express as a dependency in the package.json file and install express in the pineapple-express folder. I hope things are clear now.
In first case, all the necessary folder structure and and app.js file with the all the necessary settings to start an express application is also generated. It contains the configuration related to template engine, static file path, cookies configuration etc. Some of the dependencies like morgan, jade template engine etc are also installed by the express-generator.
In the second case, you will have to create the app.js file and write the configurations manually. This includes creating the express app.
The app.js(you can name it anything like server.js or engine.js) file contains the configuration for starting a node js server. This file is executed with node to start the server.

Answer 2

npm install -g install the package globally on your system. express-generator is a module that setup a directory to contain your express app. Creates a directory structure and adds a package.json file with express as a dependency plus other common used modules. So you just can start to write your app. Express-generator install express just locally on your app directory. that's why you have to run npm install on the created directory after creating the directory with express myapp