How to create a sleep/delay in nodejs that is Blocking?

Question

I\'m currently trying to learn nodejs and a small project I\'m working is writing an API to control some networked LED lights.

The microprocessor controlling the LED

Answer 1

I found something almost working here https://stackoverflow.com/questions/21819858/how-to-wrap-async-function-calls-into-a-sync-function-in-node-js-or-ja vascript

`function AnticipatedSyncFunction(){
    var ret;
    setTimeout(function(){
        var startdate = new Date()
        ret = "hello" + startdate;
    },3000);
    while(ret === undefined) {
       require('deasync').runLoopOnce();
    }
    return ret;    
}


var output = AnticipatedSyncFunction();
var startdate = new Date()
console.log(startdate)
console.log("output="+output);`

The unique problem is the date printed isn't correct but the process at least is sequential.

Answer 2

Node is asynchronous by nature, and that's what's great about it, so you really shouldn't be blocking the thread, but as this seems to be for a project controlling LED's, I'll post a workaraound anyway, even if it's not a very good one and shouldn't be used (seriously).

A while loop will block the thread, so you can create your own sleep function

function sleep(time, callback) {
    var stop = new Date().getTime();
    while(new Date().getTime() < stop + time) {
        ;
    }
    callback();
}

to be used as

sleep(1000, function() {
   // executes after one second, and blocks the thread
});

I think this is the only way to block the thread (in principle), keeping it busy in a loop, as Node doesn't have any blocking functionality built in, as it would sorta defeat the purpose of the async behaviour.

Answer 3

With ECMA script 2017 (supported by Node 7.6 and above), it becomes a one-liner:

function sleep(millis) {
  return new Promise(resolve => setTimeout(resolve, millis));
}

// Usage in async function
async function test() {
  await sleep(1000)
  console.log("one second has elapsed")
}

// Usage in normal function
function test2() {
  sleep(1000).then(() => {
    console.log("one second has elapsed")
  });
}

Answer 4

use Node sleep package. https://www.npmjs.com/package/sleep.

in your code you can use

var sleep = require('sleep'); 
sleep.sleep(n)

to sleep for a specific n seconds.

Answer 5

You can simply use yield feature introduced in ECMA6 and gen-run library:

let run = require('gen-run');


function sleep(time) {
    return function (callback) {
        setTimeout(function(){
            console.log(time);
            callback();
        }, time);
    }
}


run(function*(){
    console.log("befor sleeping!");
    yield sleep(2000);
    console.log("after sleeping!");
});

Answer 6

Easiest true sync solution (i.e. no yield/async) I could come up with that works in all OS's without any dependencies is to call the node process to eval an in-line setTimeout expression:

const sleep = (ms) => require("child_process")
    .execSync(`"${process.argv[0]}" -e setTimeout(function(){},${ms})`);