js-async.md

Asynchronous Functions

1. Rewrite the following function using Promises:

   function add(a, b) {
     return a + b;
   }

2. Rewrite the following function using Promises:

   function squareRoot(x) {
     if (x >= 0) {
       return Math.sqrt(x);
     } else {
       return { error: "'x' must be positive" };
     }
   }

3. Using the News API, retrieve the associated photos of the top headlines. Use axios to do all requests:

   • First register on the News API website to get an API key (it's easy).

   • Write a script to retrieve the JSON information about the top headlines for Spain.

   • Download the image of a single news article (taken form the urlToImage field) using code like this:

     axios({
       method: "get",
       url: "https://someurl.com/some-file.jpg",
       responseType: "stream",
     }).then(function (response) {
       response.data.pipe(fs.createWriteStream("/my/dir/downloaded.jpg"));
     });

     The fs package is internal to NodeJS.

   • Create an array of Promises to retrieve all photos at in parallel, using Promise.all.