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2-promisify.js
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48 lines (40 loc) · 973 Bytes
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'use strict';
// Callback-last function to Promise-returning
const promisify =
(fn) =>
(...args) =>
new Promise((resolve, reject) => {
fn(...args, (err, data) => {
if (err) reject(err);
else resolve(data);
});
});
/*
const promisify = (fn) => (...args) => {
const { promise, resolve, reject } = Promise.withResolvers();
fn(...args, (err, data) => {
if (err) reject(err);
else resolve(data);
});
return promise;
};
*/
// Usage
const twiceCallback = (x, callback) => {
callback(null, x * 2);
};
const twicePromise = promisify(twiceCallback);
const halfCallback = (x, callback) => {
callback(null, x / 2);
};
const halfPromise = promisify(halfCallback);
twiceCallback(100, (e, value) => {
halfCallback(value, (e, result) => {
console.dir({ callbackLast: result });
});
});
twicePromise(100)
.then((value) => halfPromise(value))
.then((result) => {
console.dir({ promisified: result });
});