Remove a Javascript function running with button click

Question

I have a javascript function running with button click.

<button id="lens" value="Zoom" onclick="magnify('imgL', 2);

It is a function that is in external . js, which Zoom in an image by activating a Lens on the mouse tip.

But I cannot deactivate the function. The user has to click to activate the zoom (as it is) and if they click again, DEACTIVATE the zoom.

How to remove a function (disabled) it with click of the button??

For those who want more information about the function, follow the link: Funcao Zoom Lens Javascript

Answer 1

Put an if in the function by checking the element with the class .img-magnifier-glass exists. If it exists, you remove, if not, apply the lens:

function magnify(imgID, zoom) {

    if(document.querySelectorAll(".img-magnifier-glass").length){
       document.querySelector(".img-magnifier-glass").remove();
    }else{

       // código do zoom

    }
}

Example:

function magnify(imgID, zoom) {

	if(document.querySelectorAll(".img-magnifier-glass").length){
       document.querySelector(".img-magnifier-glass").remove();
    }else{

  var img, glass, w, h, bw;
  img = document.getElementById(imgID);
  /*create magnifier glass:*/
  glass = document.createElement("DIV");
  glass.setAttribute("class", "img-magnifier-glass");
  /*insert magnifier glass:*/
  img.parentElement.insertBefore(glass, img);
  /*set 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;
  /*execute a function when someone moves the magnifier glass over the image:*/
  glass.addEventListener("mousemove", moveMagnifier);
  img.addEventListener("mousemove", moveMagnifier);
  /*and also for touch screens:*/
  glass.addEventListener("touchmove", moveMagnifier);
  img.addEventListener("touchmove", moveMagnifier);
  function moveMagnifier(e) {
    var pos, x, y;
    /*prevent any other actions that may occur when moving over the image*/
    e.preventDefault();
    /*get the cursor's x and y positions:*/
    pos = getCursorPos(e);
    x = pos.x;
    y = pos.y;
    /*prevent 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;}
    /*set the position of the magnifier glass:*/
    glass.style.left = (x - w) + "px";
    glass.style.top = (y - h) + "px";
    /*display 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;
    /*get the x and y positions of the image:*/
    a = img.getBoundingClientRect();
    /*calculate 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};
  }
  }
}

* {box-sizing: border-box;}

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

.img-magnifier-glass {
  position: absolute;
  border: 3px solid #000;
  border-radius: 50%;
  cursor: none;
  /*Set the size of the magnifier glass:*/
  width: 100px;
  height: 100px;
}

<button id="lens" value="Zoom" onclick="magnify('myimage', 2);">ZOOM</button>
<h1>Image Magnifier Glass</h1>

<p>Mouse over the image:</p>

<div class="img-magnifier-container">
  <img id="myimage" src="https://www.cleverfiles.com/howto/wp-content/uploads/2016/08/mini.jpg" width="600" height="400">
</div>