You will notice that we have a node_modules folder which is managed by our main package.json in the root. This is where we save all packages we use for operations (building, testing, etc) and backend (node + express).
But, when you run npm install you will see that a new node_modules folder is created under vendors. This folder is managed by the vendors/package.json file.
In order to install a new front-end package you need to run the normal npm i ... but being under the right path in your terminal, meaning vendors. The first step when installing a front-end package is to type
cd vendors
and then
npm i --save PACKAGE_NAME (always use --save, otherwise it won't work, since --save-dev is skipped in Heroku)
Once you had saved it into vendors/package.json, then in the same file you will find the object mainfiles. Here you have to create a new object following the format it has currently, where the property is the exact name of the package's folder (normally the same name as the package itself), and the value of this property should be an array of strings, where the name of the file/folder should always begin with a /
example:
"mainfiles": {
"jquery": [
"/dist/jquery.min.js"
]
}
Once you have included there the name of the file/s you need, you only need to run gulp and it will take care of compiling the new vendor files.
NOTE: if you never install a new package, you don't need to run gulp at all, since it is triggered once when you run npm install in the root of the repository. gulp is only useful if you already installed all packages for EOS and added/changed a FE package (development reasons)