Creating a Timestamped Object Array for Sampling Data in Javascript?

Question

Goal is to push sampled data, as an object, onto an array, at a periodic interval and wait to log the new array out to the console once it is finalized.

I'm new to JS, so take it easy ;). I am likely making this more complicated than it needs to be. Thought it would be as simple as a setTimeout() in a for loop.

I have been able to generate the array two different ways, using IIFE with a setTimeout() also the setInterval() below. Not sure how to get the async await function working with an array push() method querying length. Maybe this is not a good approach?


class Sample {
    constructor(tag, timeStamp) {
        this.tag = tag;
        this.timeStamp = Date.now();
    }
}

function arrayGenerator(tag){
    return sampleArr.push(new Sample(tag));
};

function setIntSample(callback, delay, iterations) {
    var i = 0;
    var intervalID = setInterval(function () {
       callback(i);
       if (++i === iterations) {
           clearInterval(intervalID);
       }
    }, delay);
};

Above seems to work console.log()-ing the array as it is generated in the arrayGenerator() function. Below, no dice

function resolveAfterArrGeneration(){
    return new Promise(resolve => {
        arrLength = setIntSample(i => {arrayGenerator(i)}, 3000, 5) 
        if (arrLength === 5) {resolve();}
    });
}

async function ans() {
    var answer = await resolveAfterArrGeneration();
    console.log(sampleArr);
}
ans();

Mark · Accepted Answer · 2019-04-27 19:31:50Z

1

The basic idea is to return a promise and resolve the promise when the setInterval has run enough iterations. You can do that in a single function with something like this (with extra console.logs to show the process):

class Sample {
    constructor(tag, timeStamp) {
        this.tag = tag;
        this.timeStamp = Date.now();
    }
}

function makeSamples(iterations, delay){
    let samples = [], i = 0;
    return new Promise(resolve => {
        let intervalID = setInterval(function () {
           console.log("pushing new sample")
           samples.push(new Sample('tag: ' + i));
           if (++i === iterations) {
               console.log("finished resolving")
               clearInterval(intervalID);
               resolve(samples)
           }
        }, delay);
    })
}

makeSamples(5, 1000).then(console.log)

answered Apr 27, 2019 at 19:31

Mark

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Comments

trincot · Accepted Answer · 2019-04-27 20:02:35Z

0

I would isolate the delay part (the asynchronous) part and create a separate, generic function delay() for that. All the rest becomes simple then, using an async function and for loop:

const delay = (ms) => new Promise(resolve => setTimeout(resolve, ms));

class Sample {
    constructor(tag, timeStamp) {
        this.tag = tag;
        this.timeStamp = Date.now();
    }
}

async function setIntSample(callback, ms, iterations) {
    const arr = [];
    for (let i = 0; i < iterations; i++) {
       if (i) await delay(ms); // don't delay first time
       arr.push(callback(i));
    }
    return arr;
}

const newSample = (tag) => new Sample(tag)

console.log("wait for it....");
setIntSample(newSample, 1000, 5).then(console.log);

answered Apr 27, 2019 at 20:02

trincot

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1 Comment

Jeffrey Boyer Over a year ago

Much appreciated. Looks like this would make it simple to run multiple processes in parallel at different sampling frequencies.

Jeffrey Boyer · Accepted Answer · 2019-04-28 18:32:11Z

0

Another way I just got working with a generator function

function* simpleGenerator(){
    var index = 0;
    while (true)
        yield {tag: index++, time: Date.now()} 
}
var gen = simpleGenerator();

..with the corresponding push

        arr.push(gen.next().value);

answered Apr 28, 2019 at 18:32

Jeffrey Boyer

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