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make a function that will add a fixed position button to the top left corner of the web page. the button will allow drag and dropping an image onto it, either from the local file system or from a web page. it will then display a canvas of the same size as the image, displayed at fixed position a few pixels lower than the button. it will load the canvas with the image data. it will store the canvas in global variable "myCanvas". if a second image is dropped onto the button, it will create a second canvas at a larger size, so that both images will fit, side by side. It will copy the first image onto the new canvas, and then put the second image to the right of the first. finally, it will remove the first canvas and add the second canvas in its place

Here's a sample code to achieve what you're looking for:

php
<!DOCTYPE html>
<html>
<head>
  <style>
    #myButton {
      position: fixed;
      top: 10px;
      left: 10px;
      width: 50px;
      height: 50px;
      background-color: blue;
    }
    #myCanvas {
      position: fixed;
      top: 70px;
      left: 10px;
      border: 1px solid black;
    }
  </style>
</head>
<body>
  <button id="myButton">Drop Image</button>
  <script>
    let myCanvas;
    let canvasWidth = 0;
    let canvasHeight = 0;

    function handleImageDrop(event) {
      event.preventDefault();

make a javascript function that will add a fixed position button, named "drop image here", to the top left corner of the web page. the button will allow drag and dropping an image onto it, either from the local file system or from a web page. it will then display a canvas of the same size as the image, displayed at fixed position a few pixels lower than the button. it will load the canvas with the image data. if a second image is dropped onto the button, it will create a new canvas at a larger size, so that both images will fit, side by side. It will then copy the image from the first canvas onto the new canvas, and then put the second image onto the canvas, to the right of the first image. finally, it will remove the first canvas from the document, and add the second canvas in its place

Here's a sample code to achieve what you're looking for:

php
<!DOCTYPE html>
<html>
<head>
  <style>
    #myButton {
      position: fixed;
      top: 10px;
      left: 10px;

please do the previous request purely as javascript. i want a single javascript function that will do the requirements as previously stated

Here's a single JavaScript function that implements the requirements you described:

javascript
function addImageDropButton() {
  // Create the button element
  var button = document.createElement("button");
  button.innerHTML = "Drop Image Here";
  button.style.position = "fixed";
  button.style.top = "10px";
  button.style.left = "10px";

  // Add the button to the page
  document.body.appendChild(button);

  // Handle the image drop event
  button.addEventListener("drop", function(event) {
    event.preventDefault();

    // Get the dropped image
    var image = event.dataTransfer.files[0];

    // Load the image
    var reader = new FileReader();
    reader.onload = function(event) {
      var imageData = event.target.result;

      // Create the canvas element
      var canvas = document.createElement("canvas");
      canvas.style.position = "fixed";
      canvas.style.top = "70px";
      canvas.style.left = "10px";
      canvas.style.border = "1px solid black";

      // Draw the image on the canvas
      var context = canvas.getContext("2d");
      var imageObj = new Image();
      imageObj.onload = function() {
        canvas.width = imageObj.width;
        canvas.height = imageObj.height;
        context.drawImage(imageObj, 0, 0);

        // If there is already a canvas, create a new canvas that fits both images
        if (document.getElementById("myCanvas")) {
          var oldCanvas = document.getElementById("myCanvas");
          canvas.width = oldCanvas.width + imageObj.width;
          canvas.height = Math.max(oldCanvas.height, imageObj.height);
          context.drawImage(oldCanvas, 0, 0);
          context.drawImage(imageObj, oldCanvas.width, 0);
          oldCanvas.parentNode.removeChild(oldCanvas);
        }

        canvas.id = "myCanvas";
        document.body.appendChild(canvas);
      };
      imageObj.src = imageData;
    };
    reader.readAsDataURL(image);
  });

  // Enable dragging and dropping on the button
  button.addEventListener("dragover", function(event) {
    event.preventDefault();
  });
}

To use the function, simply call addImageDropButton() in your JavaScript code.