Barrier demonstration

barrier.js

"use strict";

function longRunningFunction1(onComplete) {
    setTimeout(onComplete, 3000);
}

function longRunningFunction2(onComplete) {
    setTimeout(onComplete, 2000);
}

function executeSequentially() {
    longRunningFunction1(function() {
        longRunningFunction2(function() {
            console.log("The functions running sequentially have finished.");
        });
    });
}

function makeBarrier(onComplete) {
    var firstFinished = false;
    
    var barrier = function() { // called by each function when it finishes
        if(! firstFinished) { // first (by time) function finished
            firstFinished = true;
        } else { // second function finished
            onComplete();
        }
    };
    return barrier;
}

function executeSimultaneously() {
    var barrier = makeBarrier(function() {
        console.log("The functions running simultaneously have finished.");
    });

    longRunningFunction1(barrier);
    longRunningFunction2(barrier);
}


executeSequentially();
executeSimultaneously();


// timer
function timer(i) {
    console.log(i);
    if(i < 5) setTimeout(function() { timer(i+1); }, 1000);
}
timer(1);

what is timer at the bottom