Concatenate variable name with iterator index in for loop

Question

I am trying to create in javascript a set of buttons that makes a slider swap the images depending on what button I click.

I came up with this ugly redundant code:

var changer1 = document.getElementById("changer1");
var changer2 = document.getElementById("changer2");
var changer3 = document.getElementById("changer3");

var r = document.getElementsByClassName('carousel-item');

changer1.addEventListener('click', function() {
    for (let i = 0; i < r.length; i++) {
        r[i].classList.remove('active')
    }
    r[0].classList.add('active')
});

changer2.addEventListener('click', function() {
    for (let i = 0; i < r.length; i++) {
        r[i].classList.remove('active')
    }
    r[1].classList.add('active')
});

changer3.addEventListener('click', function() {
    for (let i = 0; i < r.length; i++) {
        r[i].classList.remove('active')
    }
    r[2].classList.add('active')
});

And it worked, but I know that redundant code can be optimized, so I tried this:

var changersArray = document.getElementsByClassName('changers');

for (let i = 0; i < 3; i++) {  
    changer[i].addEventListener('click', function() {
        for (let i = 0; i < r.length; i++) {
            r[i].classList.remove('active')
        }
        r[0].classList.add('active')
    });
}

This is the HTML:

<section class="container-fluid sectionFive">
    <div class="row title_image">
        <div class="col-sm-12">
            <h1 class="wow flipInY delay-1s slow">Testimonials</h1>
        </div>
    </div>

    <div class="row">
        <div class="col-sm-2"></div>
        <div class="col-sm-8 fetchDiv">

            <div id="carouselExampleControls" class="carousel slide wow
                    fadeIn" data-ride="carousel">
                <div class="carousel-inner">
                    <div class="carousel-item active">
                        <img class="mt-2 rounded-circle people" src="images/person_3.jpg" alt="">
                        <p class="frase"></p>
                        <p class="author"></p>

                    </div>
                    <div class="carousel-item">
                        <img class="mt-2 rounded-circle people" src="images/person_2.jpg" alt="">
                        <p class="frase"></p>
                        <p class="author"></p>

                    </div>
                    <div class="carousel-item">
                        <img class="mt-2 rounded-circle people" src="images/person_1.jpg" alt="">
                        <p class="frase"></p>
                        <p class="author"></p>
                    </div>
                </div>
                <a class="carousel-control-prev" href="#carouselExampleControls" role="button" data-slide="prev">
                    <span class="carousel-control-prev-icon" aria-hidden="true"></span>
                    <span class="sr-only">Previous</span>
                </a>
                <a class="carousel-control-next" href="#carouselExampleControls" role="button" data-slide="next">
                    <span class="carousel-control-next-icon" aria-hidden="true"></span>
                    <span class="sr-only">Next</span>
                </a>
            </div>

        </div>
        <div class="col-sm-2">

        </div>
    </div>
    <div class="row changersRow">
        <button class="changers" id="changer1">1</button><button class="changers" id="changer2">2</button><button class="changers" id="changer3">3</button>

    </div>
</section>

I was trying to dynamically create changer1, changer2, and changer3 with by writing changer[i] inside the loop but didn't work.

Please, can you help me figure out why it does not work, and how can I make it work?

Thanks.

Please share the HTML as well. Why do you have same i in inner for loop as well as in outer for loop? — Hassan Imam
– Hassan Imam, Commented Apr 22, 2019 at 11:35
I shared the HTML, please, have a look at it, and yes, I hadn't seen I was using the same index for the outer and inner loop. — Julio Rodríguez
– Julio Rodríguez, Commented Apr 22, 2019 at 11:42

malarres · Accepted Answer · 2019-04-22 11:35:38Z

2

First two improvements that come from the top of my head:

for (let i = 0; i < 3; i++) {  
  changer[i].addEventListener('click', function() {
      for (let j = 0; j < r.length; j++) {
          r[j].classList.remove('active')
      }
      r[i].classList.add('active')
  });
}

Notice the inner i replaced and the r[0] changed to use the actual index

answered Apr 22, 2019 at 11:35

malarres

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