bluebird Converting a callback API to promises. Converting a single NodeJS function

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Example

You can convert a single function with a callback argument to a Promise-returning version with Promise.promisify, so this:

const fs = require("fs");
fs.readFile("foo.txt", (err, data) => {
   if(err) throw err;
   console.log(data);
});

becomes:

const promisify = require("bluebird");
const readFile = promisify(require("fs").readFile));
readFile("foo.txt").then(console.log); // promisified version


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