JavaScript: Convert an asynchronous function to return a promise
JavaScript fundamental (ES6 Syntax): Exercise-162 with Solution
Write a JavaScript program to convert an asynchronous function to return a promise.
- Use currying to return a function returning a Promise that calls the original function.
- Use the rest operator (...) to pass in all the parameters.
- Note: In Node 8+, you can use util.promisify.
Sample Solution:
JavaScript Code:
//#Source https://bit.ly/2neWfJ2
const promisify = func => (...args) =>
new Promise((resolve, reject) =>
func(...args, (err, result) => (err ? reject(err) : resolve(result)))
);
const delay = promisify((d, cb) => setTimeout(cb, d));
delay(2000).then(() => console.log('Hi!')); // // Promise resolves after 2s
Sample Output:
Hi!
Flowchart:

Live Demo:
See the Pen javascript-basic-exercise-162 by w3resource (@w3resource) on CodePen.
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Previous: Write a JavaScript program to mutate the original array to filter out the values specified. Returns the removed elements.
Next: Write a JavaScript program to convert a number in bytes to a human-readable string.
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JavaScript: Tips of the Day
How to check whether a string contains a substring in JavaScript?
ECMAScript 6 introduced String.prototype.includes:
const string = "foo"; const substring = "oo"; console.log(string.includes(substring));
includes doesn't have Internet Explorer support, though. In ECMAScript 5 or older environments, use String.prototype.indexOf, which returns -1 when a substring cannot be found:
var string = "foo"; var substring = "oo"; console.log(string.indexOf(substring) !== -1);
Ref: https://bit.ly/3fFFgZv
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