Well actually I did it, but with a kind of bypass:
I wrote a js file with my scripts. Then I created a project and created a call to a function where all my scripts are developed.
Then, I edited the resulting index.html in order to include there the js file where my function is.
And that's all!
It works for my aim, which was just to employ the jsPDF.js library to create a PDF form presenting data from my construct app.