Problem with Function or Events in JavaScript code

Question

I was writing this application in HTML , CSS and Javascript that creates a magnifier glass that will be used in one of 3 images (choosen by the user), but when i change from one image to another, using a Combobox the magnifier glass becomes awkward (repeats itself).

I tried to change the code in several ways but i still didn't found what's wrong with it!?

Here's the code:

<head>
    <meta name="viewport" content="width=device-width, initial-scale=1.0">

    <!-- CSS Code -->
    <style>
        *
        {
            box-sizing: border-box;
        }

        .img-magnifier-container
        {
            position:relative;
        }

        .img-magnifier-glass
        {
            position: absolute;
            border: 3px solid #000000;
            border-radius: 50%;
            cursor: none;
            /* Sets the size of the Magnifier Glass. */
            width: 100px;
            height: 100px;
        }
    </style>

    <!-- JavaScript Code -->
    <script>
        function magnify(imgID, zoom)
        {
            var img, glass, w, h, bw;
            img = document.getElementById(imgID);
            // Creates the Magnifier Glass.
            glass = document.createElement("DIV");
            glass.setAttribute("class", "img-magnifier-glass");
            // Inserts the Magnifier Glass.
            img.parentElement.insertBefore(glass, img);
            // Sets the Background Properties for the Magnifier Glass.
            glass.style.backgroundImage = "url('" + img.src + "')";
            glass.style.backgroundRepeat = "no-repeat";
            glass.style.backgroundSize = (img.width * zoom) + "px " + (img.height * zoom) + "px";
            bw = 3;
            w = glass.offsetWidth / 2;
            h = glass.offsetHeight / 2;
            // Executes the "moveMagnifier" Function when someone moves the Magnifier Glass over the Image.
            glass.addEventListener("mousemove", moveMagnifier);
            img.addEventListener("mousemove", moveMagnifier);

            function moveMagnifier(e)
            {
                var pos, x, y;
                // Prevents any other actions that may occur when moving over the Image.
                e.preventDefault();
                // Gets the Cursor's x and y Positions.
                pos = getCursorPos(e);
                x = pos.x;
                y = pos.y;
                // Prevents the Magnifier Glass from being positioned outside the Image.
                if (x > img.width - (w / zoom))
                    x = img.width - (w / zoom);
                if (x < w / zoom)
                    x = w / zoom;
                if (y > img.height - (h / zoom))
                    y = img.height - (h / zoom);
                if (y < h / zoom)
                    y = h / zoom;
                // Sets the position of the Magnifier Glass.
                glass.style.left = (x - w) + "px";
                glass.style.top = (y - h) + "px";
                // Displays what the Magnifier Glass sees.
                glass.style.backgroundPosition = "-" + ((x * zoom) - w + bw) + "px -" + ((y * zoom) - h + bw) + "px";
            }

            function getCursorPos(e)
            {
                var a, x = 0, y = 0;
                e = e || window.event;
                // Gets the x and y Positions of the Image.
                a = img.getBoundingClientRect();
                // Calculates the Cursor's x and y Coordinates, relative to the Image.
                x = e.pageX - a.left;
                y = e.pageY - a.top;
                // Consider any page scrolling.
                x = x - window.pageXOffset;
                y = y - window.pageYOffset;
                return {x : x, y : y};
            }
        }
        </script>
    </head>


<body>
    <h1>Image Magnifier Glass</h1>

    <select id="CBFotos">
        <option value="foto1.jpg">Foto 1</option>
        <option value="foto2.jpg">Foto 2</option>
        <option value="foto3.jpg">Foto 3</option>
    </select>

    <br><br><br>

    <div class="img-magnifier-container">
        <img id="foto" src="foto1.jpg" width="600" height="400">
    </div>

    <script>
        // The User can choose from 3 Photos to use with the Magnifier Glass.
        // When there is a change in the selected Item of the ComboBox, the "onchange" Event is triggered, and the declared Function is executed.
        document.getElementById("CBFotos").onchange = function()
        {
            var comboBoxFotos = document.getElementById("CBFotos");
            // Puts the new ComboBox's Selected Value in the "src" Attribute of the Img Element with the "id=foto".
            document.getElementById("foto").attributes["src"].value = comboBoxFotos.options[comboBoxFotos.selectedIndex].value;
            magnify("foto", 3);
        };

        // Calls the "magnify" Function with the "id" of the Image, and the strength of the Magnifier Glass.
        magnify("foto", 3);
    </script>
</body>

Well every time you call magnify() (each time you change the comboBox), you create a new div - which holds a new magnifying glass. It is doing what you've told it to do. — Randy Casburn
– Randy Casburn, Commented Jun 18, 2019 at 17:58

Paulo Roberto Dalmas Junior · Accepted Answer · 2019-06-18 18:28:32Z

1

As Randy says, you must remove your magnifier before create other.

I've updated your "onchange" code with a solution:

document.getElementById("CBFotos").onchange = function() {
  var comboBoxFotos = document.getElementById("CBFotos");
  // Puts the new ComboBox's Selected Value in the "src" Attribute of the Img Element with the "id=foto".
  document.getElementById("foto").attributes["src"].value = comboBoxFotos.options[comboBoxFotos.selectedIndex].value;

  var magnifyEl = document.getElementsByClassName("img-magnifier-glass")[0];
  magnifyEl.parentNode.removeChild(magnifyEl);

  magnify("foto", 3);
};

answered Jun 18, 2019 at 18:28

Paulo Roberto Dalmas Junior

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2 Comments

Pedro Figueiredo Over a year ago

Thank you Randy. Obrigado Paulo. Funcionou ás mil maravilhas. Andei lá perto mas... não acertei bem no target!

Paulo Roberto Dalmas Junior Over a year ago

Perfeito Pedro,, fico feliz que tenha funcionado bem.. abraço

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