Reputation:

How do I only allow an item to be dropped in a certain place in HTML/JavaScript?

StackOverflow community! For the past few weeks, I have been working on a drag-and-drop for HTML/JavaScript. Basically, I have a circle and two boxes. The circle can be dragged to anywhere on the screen. However, I need it so the circle can only be dropped within one of the two boxes. Despite several days of research, I could not figure out how to do this. Thank you in advance!

<!DOCTYPE html>
<html>

<head>
  <meta name="viewport" 
        content="width=device-width, 
        initial-scale=1.0, 
        user-scalable=no" />
  <title>Drag/Drop/Bounce</title>
  <style>
    #item {
      width: 100px;
      height: 100px;
      background-color: rgb(245, 230, 99);
      border: 10px solid rgba(136, 136, 136, .5);
      border-radius: 50%;
      touch-action: none;
      user-select: none;
    }
    
    #box1 {
      width: 200px;
      height: 200px;
      background-color: red;
    }
    
    #box2 {
      width: 200px;
      height: 200px;
      background-color: lightblue;
    }
  </style>
</head>

<body>
<h1>Drag and Drop</h1>
<div id="box1">
  <div id="item"></div>
</div>
<br>
<div id="box2"></div>

  <script>
    var dragItem = document.querySelector("#item");
    var container = dragItem;
    
    //Declare Variables
    var active = false;
    var currentX;
    var currentY;
    var initialX;
    var initialY;
    var xOffset = 0;
    var yOffset = 0;
    
    //Add Event Listeners for Touchscreens
    container.addEventListener("touchstart", dragStart, false);
    container.addEventListener("touchend", dragEnd, false);
    container.addEventListener("touchmove", drag, false);
    
    //Add Event Listeners for Mice
    container.addEventListener("mousedown", dragStart, false);
    container.addEventListener("mouseup", dragEnd, false);
    container.addEventListener("mousemove", drag, false);

    function dragStart(e) { //when the drag starts
      if (e.type === "touchstart") { //if its a touchscreen
        initialX = e.touches[0].clientX - xOffset; //set initial x-cordinate to where it was before drag started
        initialY = e.touches[0].clientY - yOffset; //set initial y-cordinate to where it was before drag started
      } else { //if its not a touchscreen (mouse)
        initialX = e.clientX - xOffset; //set initial x-cordinate to where it was before drag started
        initialY = e.clientY - yOffset; //set initial y-cordinate to where it was before drag started
      }

      if (e.target === dragItem) { //if user is dragging circle
        active = true; //the drag is active
      }
    }

    function dragEnd(e) { //when the drag ends
      initialX = currentX; //set the initial x-cordinate to where it is now
      initialY = currentY; //set the initial y-cordinate to where it is now
      
      active = false; //the drag is no longer active
    }

    function drag(e) { //when the circle is being dragged
      if (active) { //if the drag is active
        e.preventDefault(); //the user cant do anything else but drag
      
        if (e.type === "touchmove") { //if its a touchscreen
          currentX = e.touches[0].clientX - initialX; //set current x-cordinate to where it is now
          currentY = e.touches[0].clientY - initialY; //set current y-cordinate to where it is now
        } else { //if its not a touchscreen (mouse)
          currentX = e.clientX - initialX; //set current x-cordinate to where it is now
          currentY = e.clientY - initialY; //set current y-cordinate to where it is now
        }
        
        //Im not sure what this does but it dosnt work without it
        xOffset = currentX;
        yOffset = currentY;
        setTranslate(currentX, currentY, dragItem);
      }
    }

    function setTranslate(xPos, yPos, el) { //Im not sure what this does but it dosnt work without it
      el.style.transform = "translate3d(" + xPos + "px, " + yPos + "px, 0)";
    }
  </script>
</body>

</html>

I've also uploaded the code to TryIt for those who prefer: https://www.w3schools.com/code/tryit.asp?filename=GCF4V2RIT7T4

Upvotes: 1

Answers (1)

Johnny Zabala

Reputation: 2465

In this version you can move the circle only inside the red box. I think you can take that and easily implement the other box.

<!DOCTYPE html>
<html>

<head>
  <meta name="viewport" 
    content="width=device-width, 
    initial-scale=1.0, 
    user-scalable=no" />
  <title>Drag/Drop/Bounce</title>
  <style>
#item {
  width: 100px;
  height: 100px;
  background-color: rgb(245, 230, 99);
  border: 10px solid rgba(136, 136, 136, .5);
  border-radius: 50%;
  touch-action: none;
  user-select: none;
  position: absolute;
}

#box1 {
  width: 200px;
  height: 200px;
  background-color: red;
}

#box2 {
  width: 200px;
  height: 200px;
  background-color: lightblue;
}
  </style>
</head>

<body>
<h1>Drag and Drop</h1>
<div id="item"></div>
<div id="box1">
</div>
<br>
<div id="box2"></div>

  <script>
var dragItem = document.querySelector("#item");
var box1 = document.querySelector("#box1");
var box2 = document.querySelector("#box2");
var container = dragItem;
//Declare Variables
var active = false;
var currentX;
var currentY;
var initialX;
var initialY;
var xOffset = 0;
var yOffset = 0;

//Add Event Listeners for Touchscreens
container.addEventListener("touchstart", dragStart, false);
container.addEventListener("touchend", dragEnd, false);
container.addEventListener("touchmove", drag, false);

//Add Event Listeners for Mice
container.addEventListener("mousedown", dragStart, false);
container.addEventListener("mouseup", dragEnd, false);
container.addEventListener("mousemove", drag, false);

function dragStart(e) { //when the drag starts
  if (e.type === "touchstart") { //if its a touchscreen
    initialX = e.touches[0].clientX - xOffset; //set initial x-cordinate to where it was before drag started
    initialY = e.touches[0].clientY - yOffset; //set initial y-cordinate to where it was before drag started
  } else { //if its not a touchscreen (mouse)
    initialX = e.clientX - xOffset; //set initial x-cordinate to where it was before drag started
    initialY = e.clientY - yOffset; //set initial y-cordinate to where it was before drag started
  }
  if (e.target === dragItem) { //if user is dragging circle
    active = true; //the drag is active
  }
}

function dragEnd(e) { //when the drag ends
  const box1Size = box1.getBoundingClientRect()
  const elementSize = dragItem.getBoundingClientRect()
  if (elementSize.left >= box1Size.left && elementSize.right <= box1Size.right && elementSize.top >= box1Size.top && elementSize.bottom <= box1Size.bottom) {
    initialX = currentX; //set the initial x-cordinate to where it is now
    initialY = currentY; //set the initial y-cordinate to where it is now
  } else {
   	currentX = 0
    currentY = 0
	initialX = 0
    initialY = 0
    xOffset = 0;
    yOffset = 0;
  	setTranslate(0, 0, dragItem);
  }
  
  active = false; //the drag is no longer active
}

function drag(e) { //when the circle is being dragged
  if (active) { //if the drag is active
    e.preventDefault(); //the user cant do anything else but drag
  
    if (e.type === "touchmove") { //if its a touchscreen
      currentX = e.touches[0].clientX - initialX; //set current x-cordinate to where it is now
      currentY = e.touches[0].clientY - initialY; //set current y-cordinate to where it is now
    } else { //if its not a touchscreen (mouse)
      currentX = e.clientX - initialX; //set current x-cordinate to where it is now
      currentY = e.clientY - initialY; //set current y-cordinate to where it is now
    }
    
    //Im not sure what this does but it dosnt work without it
    xOffset = currentX;
    yOffset = currentY;
    setTranslate(currentX, currentY, dragItem);
  }
}

function setTranslate(xPos, yPos, el) { //Im not sure what this does but it dosnt work without it
  el.style.transform = "translate3d(" + xPos + "px, " + yPos + "px, 0)";
}
  </script>
</body>

</html>

Upvotes: 1

How do I only allow an item to be dropped in a certain place in HTML/JavaScript?

Answers (1)

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