javascript: displaying image according to select box value

Question

In my program I have created select box and button. upon selecting different value from select box image should be displayed as shown in expected output. There are two buttons previous and next to change images. which should also work accordingly. I have created code below but my code is not working as per expectation. Can anyone help me ?

code:

// counter
var i = 0;

// create object
imageObj = new Image(128, 128);

// set image list
images = new Array();
images[0] = "final_images/wcoat.jpg";
images[1] = "final_images/wcoat.jpg";
images[2] = "final_images/ktoys.jpg";
images[3] = "final_images/mixture.jpeg";
images[4] = "final_images/earing.jpg";

var imgLen = imageObj.length;

var go = document.getElementById('go');
go.addEventListener("click", loadItem);

function loadItem() {

  var mainDiv = document.getElementById("main");

  var btnPre = document.createElement("input");
  //Assign different attributes to the element. 
  btnPre.type = "button";
  btnPre.value = "previous";
  btnPre.id = "preBtn";

  mainDiv.appendChild(btnPre);

  preBtn.addEventListener('click', prvs);

  var holder = document.getElementById("holder");

  if (document.getElementById('selectBox').value == "womens") {
    holder.src = images[0] + "<br>" + " Women's coat";
  } else if (document.getElementById('selectBox').value == "mens") {
    holder.src = images[1] + "<br>" + " Men's coat";
  } else if (document.getElementById('selectBox').value == "kids") {
    holder.src = images[2] + "<br>" + " Kid's toys";
  } else if (document.getElementById('selectBox').value == "mixture") {
    holder.src = images[3] + "<br>" + " Classic mixture";
  } else if (document.getElementById('selectBox').value == "earing") {
    holder.src = images[4] + "<br>" + " Gold Earing";
  }

  var btnNxt = document.createElement("input");
  //Assign different attributes to the element. 
  btnNxt.type = "button";
  btnNxt.value = "next";
  btnNxt.id = "nxtBtn";

  mainDiv.appendChild(btnNxt);

  nxtBtn.addEventListener('click', nxt);
}

function nxt() {
  if (i < imgLen - 1) {
    i++;
  } else {
    i = 0;
  }

  imageObj.src = images[i];
}

function prvs() {
  if (i > 0) {
    i--;
  } else {
    i = imgLen - 1;
  }
  imageObj.src = images[i];
}

body {
  background-image: url("final_images/back.jpg");
}

.container {
  /*width: 600px;*/
  /*height: 200px;*/
  border: inset;
  background-color: rgba(255, 234, 134, 0.9);
}

#selectBox {
  margin-left: 210px;
  width: 160px;
}

#below_hr {
  width: 600px;
  background-color: #ffffff;
}

#preBtn {
  margin-left: 170px;
  margin-top: 170px;
}

<div class='container' id="main">
  <form name="myForm">
    <select name="mySelect" id="selectBox">
        				<option value="womens">Women's coat</option>
        				<option value="mens">Men's coat</option>
        				<option value="kids">Kid's toys</option>
        				<option value="mixture">Classic mixture</option>
        				<option value="earing">Gold Earing</option>
        			</select>
    <INPUT TYPE="button" VALUE="Go" id="go">
    </INPUT>
  </form>
  <HR size="4" color="red" id="hr">

  <div id="holder"> </div>
</div>

Answer 1

You have quite a few errors inside your code, Andrew (+1 for that) already listed them in his answer. But i think you maybe should also try to be more dynamic and create the selection from for example a configuration object.

Here's an example:

// CLASS
var ImageSelector = (function(doc) {
  // private variables
  var _config,
      _selectionEl, 
      _imageEl,
      _prevBtnEl,
      _nextBtnEl,
      _currentIndex = 0;
  
  // constructor
  function ImageSelector(config) {
    var imageholderEl = doc.querySelector(config.imageholder);
    _config = config;
    _selectionEl = doc.querySelector(config.selection);
    _prevBtnEl = doc.querySelector(config.prevBtn);
    _nextBtnEl = doc.querySelector(config.nextBtn);
    if(!_selectionEl || !imageholderEl) {
      throw new Error('no selection or imageholder element found');
    }
    _imageEl = new Image();
    imageholderEl.appendChild(_imageEl);
    _generateSelection();
    _bindEvents();
  }
  
  // private methods
  function _generateSelection() {
    var fragment = doc.createDocumentFragment();
    var items = _config.items;
    
    for(var i = 0; i < items.length; ++i) {
      var item = items[i];
      var option = doc.createElement('option');
      option.value = item.value;
      option.textContent = item.name;
      fragment.appendChild(option);
    }
    _selectionEl.appendChild(fragment);
    _selectionEl.selectedIndex = _currentIndex;
  }

  function _loadImage() {
    var items = _config.items;
    var item = items.find(itm => itm.value === _selectionEl.value);
    _imageEl.src = item.image;
    _prevBtnEl.style.display = null;
    _nextBtnEl.style.display = null;
  }
  
  function _bindEvents() {
    var goBtnEl = doc.querySelector(config.goBtn);  
    _selectionEl.addEventListener('change', _loadImage);
    if(_prevBtnEl) {
      _prevBtnEl.addEventListener('click', ImageSelector.prototype.prev);
      _prevBtnEl.style.display = 'none';
    }
    if(_nextBtnEl) {
      _nextBtnEl.addEventListener('click', ImageSelector.prototype.next);
      _nextBtnEl.style.display = 'none';
    }   
    goBtnEl && goBtnEl.addEventListener('click', _loadImage)
  }
  
  function _changeIndex(direction) {
    var length = _config.items.length;
    _currentIndex = (_currentIndex + direction) % length;
    if(_currentIndex < 0) _currentIndex = length -1;
    _selectionEl.selectedIndex = _currentIndex;
    _selectionEl.dispatchEvent(new Event('change'));
  }
  
  // public methods
  ImageSelector.prototype.next = function() {
    _changeIndex(1);
  }

  ImageSelector.prototype.prev = function() {
    _changeIndex(-1);
  }

  return ImageSelector;
})(document);


// CONFIGURATION
var config = {
  selection: '#selectBox',
  imageholder: '#holder',
  goBtn: '#go',
  prevBtn: '#prev',
  nextBtn: '#next',
  items: [
    { name: "Women's coat", value: "womens", image: "https://thumb7.shutterstock.com/display_pic_with_logo/562036/116906134/stock-photo-portrait-of-brown-eyed-cat-isolated-on-white-background-116906134.jpg" },
    { name: "Men's coat", value: "mens", image: "https://thumb1.shutterstock.com/display_pic_with_logo/154447/235089946/stock-photo-cute-little-red-kitten-sleeps-on-fur-white-blanket-235089946.jpg" },
    { name: "Kid's toys", value: "kids", image: "https://thumb9.shutterstock.com/display_pic_with_logo/2288597/574871668/stock-photo-brown-cat-playing-relaxed-on-the-mobile-574871668.jpg" },
    { name: "Classic mixture", value: "mixture", image: "https://thumb9.shutterstock.com/display_pic_with_logo/4363153/520870675/stock-photo-lovely-cat-in-human-hands-vintage-effect-love-for-the-animals-520870675.jpg" },
    { name: "Gold Earing", value: "earing", image: "https://thumb9.shutterstock.com/display_pic_with_logo/428239/454556905/stock-photo-happy-scottish-kitten-looking-at-camera-isolated-on-white-background-454556905.jpg" }
  ]
}

// INITIALISATION
var selector = new ImageSelector(config);

body {
  background-image: url("final_images/back.jpg");
}

img {
  width: 200px;
}

.container {
  /*width: 600px;*/
  /*height: 200px;*/
  border: inset;
  background-color: rgba(255, 234, 134, 0.9);
}

#selectBox {
  margin-left: 210px;
  width: 160px;
}

#below_hr {
  width: 600px;
  background-color: #ffffff;
}

#preBtn {
  margin-left: 170px;
  margin-top: 170px;
}

<div class='container' id="main">
  <form name="myForm">
    <select name="mySelect" id="selectBox">
      
    </select>
    <input type="button" value="Go" id="go" />
  </form>
  <hr size="4" color="red" id="hr" />

  <div id="holder"></div>
  
  <button id="prev">Previous</button>
  <button id="next">Next</button>
</div>

Answer 2

There are a few tiny errors all adding up to this not working, I'll try to remember and point them out. Here is a working example with only 2 images -you can fill yours back in

1. you have a div for your image "holder" this should be an <img /> tag
2. var imgLen = imageObj.length; should be var imgLen = images.length; use the length of your array not the obj.
3. preBtn.addEventListener should be btnPre. preBtn doesn't exist
4. holder.src = images[0] + "<br>" + " Women's coat"; the src attribute needs to be a valid url and you mess that up when you append <br> and a string to it.
5. imageObj.src=images[i]; needs to reference your "holder" not imageObj so it should be document.getElementById("holder").src = images[i];
6. You don't need to dynamically put the next and previous buttons each image load (you aren't even clearing them) so the DOM keeps piling up with buttons.
7. You should use numbers as values so you can set the select to the correct description on next and prev
8. you need to keep track of i when the user jumps on the select (set i on the select change)

// counter
var i = 0;

// create object
imageObj = new Image(128, 128);

// set image list
images = new Array();
images[0] = "https://cdn-image.myrecipes.com/sites/default/files/summer-sweet-lemonade-cl.jpg";
images[1] = "http://www.greatamericancookies.com/app/themes/greatamericancookies/library/images/home/carousel3.png";
images[2] = "final_images/ktoys.jpg";
images[3] = "final_images/mixture.jpeg";
images[4] = "final_images/earing.jpg";

var imgLen = images.length;

var go = document.getElementById('go');
var select = document.getElementById('selectBox');
var desc = document.getElementById('desc');
go.addEventListener("click", loadItem);

function loadItem() {
  var holder = document.getElementById("holder");

  if (document.getElementById('selectBox').value == 0) {
    holder.src = images[0];
    desc.innerHTML = document.getElementById("select0").getAttribute("data-desc");
    i = 0;
  } else if (document.getElementById('selectBox').value == 1) {
    holder.src = images[1];
    desc.innerHTML = document.getElementById("select1").getAttribute("data-desc");
    i = 1;
  } else if (document.getElementById('selectBox').value == 2) {
    holder.src = images[2];
    desc.innerHTML = document.getElementById("select2").getAttribute("data-desc");
    i = 2;
  } else if (document.getElementById('selectBox').value == 3) {
    holder.src = images[3];
    desc.innerHTML = document.getElementById("select3").getAttribute("data-desc");
    i = 3;
  } else if (document.getElementById('selectBox').value == 4) {
    holder.src = images[4];
    desc.innerHTML = document.getElementById("select4").getAttribute("data-desc");
    i = 4;
  }
  document.getElementById('prev').style.display = "";
  document.getElementById('next').style.display = "";
}

function nxt() {
  if (i < imgLen - 1) {
    i++;
  } else {
    i = 0;
  }
  select.value = i;
  desc.innerHTML = document.getElementById("select" + i).getAttribute("data-desc");
  document.getElementById("holder").src = images[i];
}

function prvs() {
  if (i > 0) {
    i--;
  } else {
    i = imgLen - 1;
  }
  select.value = i;
  desc.innerHTML = document.getElementById("select" + i).getAttribute("data-desc");
  document.getElementById("holder").src = images[i];
}

body {
  background-image: url("final_images/back.jpg");
}

img {
  width: 200px;
}

.container {
  /*width: 600px;*/
  /*height: 200px;*/
  border: inset;
  background-color: rgba(255, 234, 134, 0.9);
}

#selectBox {
  margin-left: 210px;
  width: 160px;
}

#below_hr {
  width: 600px;
  background-color: #ffffff;
}

#preBtn {
  margin-left: 170px;
  margin-top: 170px;
}

<div class='container' id="main">
  <form name="myForm">
    <select name="mySelect" id="selectBox">
    				<option id="select0" data-desc="a womans coat" value=0>Women's coat</option>
    				<option id="select1" data-desc="a mens winter coat" value=1>Men's coat</option>
    				<option id="select2" data-desc="a kids toy to play with" value=2>Kid's toys</option>
    				<option id="select3" data-desc="a classic mixture" value=3>Classic mixture</option>
    				<option id="select4" data-desc="a beautiful gold earing" value=4>Gold Earing</option>
    			</select>
    <INPUT TYPE="button" VALUE="Go" id="go">
    </INPUT>
  </form>
  <HR size="4" color="red" id="hr">

  <img id="holder" /><br/>
  <span id="desc"></span><br/><br/>
  
  <button id="prev" onclick="prvs()" style="display:none">Previous</button>
  <button id="next" onclick="nxt()" style="display:none">Next</button>
</div>