Hemanth.HM

A Computer Polyglot, CLI + WEB ♥'r.

Promisified Node Builtins

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At any point in time if you were to promisify a function you can use util.promisify, for example:

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import util from "util";
import fs from "fs";

const readFile = util.promisify(fs.readFile);

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readFile("/tmp/foo.txt", "utf-8")
    .then((buffer) => {
        // we have the content
    })
    .catch((error) => {
        // Handle the error
    });

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// Maybe
(async () => {
    const content = await readFile("/tmp/foo.txt", "utf-8").catch((err) => {});
})();

But interesting there are few builtins that are already promisifed for us:

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require("module")
.builtinModules
.filter((module) => /promises/.test(module));
// -> [ 'dns/promises', 'fs/promises', 'stream/promises', 'timers/promises' ]

In the latest version of node v16 we have the below:

Sample usage:

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// mjs
import { setTimeout, setImmediate, setInterval } from "timers/promises";

const res = await setTimeout(100, "42");

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const dnsPromises = require("dns/promises"); // require('dns').promises
const lookup = dnsPromises.lookup;
const lookupResp = await lookup("127.0.1.1");
// lookupResp -> { address: '127.0.1.1', family: 4 }

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const { pipeline } = require("stream/promises");
const fs = require("fs");

async function convert() {
    await pipeline(
        fs.createReadStream("enlgish.txt"),
        async function* (source) {
            source.setEncoding("utf8");
            for await (const chunk of source) {
                yield translate(chunk, "EN2FR"); // imaginary translate method
            }
        },
        fs.createWriteStream("french.txt")
    );
    console.log("Pipeline ✅.");
}

run().catch(console.error);

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const readFile = require("fs/promises").readFile;
(async () => {
    const content = await readFile("/tmp/foo.txt", "utf-8").catch((err) => {});
})();

Hope to see more such built-in promise APIs!

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