about util.promisify()

Author: SKindij

README.md

@@ -407,3 +407,37 @@ Use ``nextTick()`` when you want to make sure that in next event loop iteration
  Did you notice how **async functions** are different compared to a **promise.then**? The ``await`` keyword suspends the ``async function``, whereas the ``Promise`` body would've kept on being executed if we would've used ``.then``!
 
  Read more in the [section with code examples](https://github.com/SKindij/Asynchronous-Programming-Node.js/tree/main/codeSamples)...
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+ ``util.promisify()`` is utility that allows you to convert function that uses Node.js-style callback pattern into function that returns promise.\
+> _Node.js-style callbacks usually follow pattern of having error object as first argument and result as second argument, like this:_
+> > ```javascript
+> > function readFile(path, callback) {
+> > fs.readFile(path, (err, data) => {
+> > if (err) {
+> > callback(err, null);
+> > } else {
+> > callback(null, data);
+> > }
+> > });
+> > }
+> > ```
+> _With util.promisify(), you can convert this function into promise-based function, like this:_
+> > ```javascript
+> > const util = require('util');
+> > const fs = require('fs');
+> > // to convert fs.readFile() into promise-based function readFile
+> > const readFile = util.promisify(fs.readFile);
+> > 
+> > async function example() {
+> > try {
+> > // to wait for data to be read from file before logging it to console
+> > const data = await readFile('path/to/file.txt');
+> > console.log(data.toString());
+> > } catch (err) {
+> > console.error(err);
+> > }
+> > }
+> > ```
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