Code #3851

Draggable Element JavaScript Implementation

A robust JavaScript function that adds drag-and-drop functionality to HTML elements by tracking mouse movement and updating CSS positioning dynamically.

JavaScript

/*
 * Function: makeDraggable
 * Description: Enables smooth drag-and-drop functionality for a target HTML element.
 * 
 * Key logic:
 * 1. Captures the initial mouse coordinates on 'mousedown'.
 * 2. Calculates the delta (change) in mouse position during 'mousemove'.
 * 3. Updates the element's 'top' and 'left' CSS properties based on the delta.
 * 4. Cleans up event listeners on 'mouseup' to prevent memory leaks or stuck movement.
 * 
 * Note: The element MUST have 'position: absolute' or 'position: fixed' in its CSS to move.
 */
function makeDraggable(element) {
  // pos1 and pos2 track the change in mouse position
  // pos3 and pos4 track the previous mouse position
  let pos1 = 0, pos2 = 0, pos3 = 0, pos4 = 0;

  // If the element contains a header or specific drag-handle class, use that for grabbing
  // otherwise, the entire element is the handle.
  const handle = element.querySelector('.drag-handle') || element;

  // Initialize the mouse down event
  handle.onmousedown = dragMouseDown;

  function dragMouseDown(e) {
    e = e || window.event;
    e.preventDefault();

    // Get the starting cursor position
    pos3 = e.clientX;
    pos4 = e.clientY;

    // Attach global listeners for movement and release
    // We attach to 'document' so the drag continues even if the mouse leaves the element boundary
    document.onmouseup = closeDragElement;
    document.onmousemove = elementDrag;
  }

  function elementDrag(e) {
    e = e || window.event;
    e.preventDefault();

    // Calculate the distance the cursor has moved since the last frame
    pos1 = pos3 - e.clientX;
    pos2 = pos4 - e.clientY;
    
    // Update 'previous' position for the next frame calculation
    pos3 = e.clientX;
    pos4 = e.clientY;

    // Update the element's style coordinates
    // offsetTop/offsetLeft represent the current relative coordinates
    element.style.top = (element.offsetTop - pos2) + 'px';
    element.style.left = (element.offsetLeft - pos1) + 'px';
  }

  function closeDragElement() {
    // Clear listeners when the mouse button is released
    document.onmouseup = null;
    document.onmousemove = null;
  }
}

// Usage Example:
// const myBox = document.getElementById('myBox');
// makeDraggable(myBox);

Prompt: A function for making HTML divs draggable

Gemini 3 Flash Preview

Code #3851

Draggable Element JavaScript Implementation

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