如何限制div拖动空间？ （没有jQuery）

Question

我想限制可拖动div在另一个div中的移动；这是通过以下代码完成的：

  <script src="https://ajax.aspnetcdn.com/ajax/jQuery/jquery-3.3.1.min.js"></script>
  <script src="http://code.jquery.com/jquery-1.9.1.js"></script>
  <script src="http://code.jquery.com/ui/1.10.1/jquery-ui.js"></script>
  <style>
  #modalPar { width: 300px; height: 150px; padding: 0.5em; border: 1px solid black}
  #myModal {width: 200px; border: 1px solid black}
  </style>
  <script>
  $(function() {
    $("#modalPar").draggable();
    $("#myModal").draggable({containment: "parent"});});
</script>

<div id="modalPar">Parent
<div id="myModal">Child</div></div>

我想在没有jQuery的情况下完成相同的任务。尝试了以下方法：

dragElement(document.getElementById("myModal"));

function dragElement(elmnt) {
  var pos1 = 0, pos2 = 0, pos3 = 0, pos4 = 0;
  if (document.getElementById(elmnt.id + "header")) {
  document.getElementById(elmnt.id + "header").onmousedown = dragMouseDown;} 
  else {elmnt.onmousedown = dragMouseDown;}

  function dragMouseDown(w) {
    w = w || window.event;
    w.preventDefault();
    pos3 = w.clientX;
    pos4 = w.clientY;
    document.onmouseup = closeDragElement;
    document.onmousemove = elementDrag;}
    
  function elementDrag(w) {
    w = w || window.event;
    w.preventDefault();
    pos1 = pos3 - w.clientX;
    pos2 = pos4 - w.clientY;
    pos3 = w.clientX;
    pos4 = w.clientY;
    elmnt.style.top = (elmnt.offsetTop - pos2) + "px";
    elmnt.style.left = (elmnt.offsetLeft - pos1) + "px";}

  function closeDragElement() {
    document.onmouseup = null;
    document.onmousemove = null;}}

#myModal {
    position: absolute;
    z-index: 9;
    background-color: #f1f1f1;
    text-align: center;
    border: 1px solid #d3d3d3;
    top: 0; right: 0; width: 110px; height: 160px}
#myModalheader {
    padding: 10px;
    cursor: move;
    z-index: 10;
    background-color: #2196F3;
    color: #fff;}

<div id="myModal">
  <div id="myModalheader">Click here to move</div>
  <p>Move</p><p>this</p><p>DIV</p>
</div>

可以通过拖动标头拖动div，该标头包含在要拖动的整个div中，但会溢出父div。 JavaScript如何防止这种情况发生？

感谢您的帮助。

Answer 1

这是一个选项；我不能认为它像jQuery一样健壮或与浏览器兼容，但是它应该显示出总体思路。我使用一个句柄变量dragged，并使用了几个类来区分draggable和draggable-child元素。有一个简单的儿童边界检查。对于填充和您要考虑的其他事项，它是相当可调整的。

let dragged;

document.addEventListener("mouseup", e => dragged = null);
document.addEventListener("mousedown", e => {
  if (e.target.classList.contains("draggable-handle")) {
    dragged = e.target.parentElement;
  }
});

document.addEventListener("mousemove", e => {    
  if (dragged) {
    e.preventDefault();
    const x = +(dragged.style.left.match(/-?\d+/g) || 0) + e.movementX;
    const y = +(dragged.style.top.match(/-?\d+/g) || 0) + e.movementY;
    const w = dragged.getBoundingClientRect().width;
    const h = dragged.getBoundingClientRect().height;

    if (dragged.classList.contains("draggable-child")) {
      const r = dragged.parentElement.getBoundingClientRect();
      const pw = r.width;
      const ph = r.height;

      if (x < 0 || y < 0 || x + w >= pw || y + h >= ph) {
        return;
      }
    }

    dragged.style.top = `${y}px`;
    dragged.style.left = `${x}px`;
  }
});

#modalPar {
  width: 300px;
  height: 150px;
  border: 1px solid black
}

#myModal {
  width: 200px;
  height: 100px;
  border: 1px solid black
}

.draggable, .draggable-child, .draggable-handle {
  position: absolute;
}

.draggable-handle {
  padding: 0.3em;
  background: black;
  color: white;
  cursor: grab;
}

<div id="modalPar" class="draggable">
  <div class="draggable draggable-handle">[drag]</div>
  <div id="myModal" class="draggable draggable-child">
    <div class="draggable draggable-handle">[drag]</div>
  </div>
</div>

Answer 2

请找到以下使用javascript（无ajax）拖动的示例

//Make the DIV element draggagle:
dragElement(document.getElementById("mydiv"));

function dragElement(elmnt) {
  var pos1 = 0, pos2 = 0, pos3 = 0, pos4 = 0;
  if (document.getElementById(elmnt.id + "header")) {
    /* if present, the header is where you move the DIV from:*/
    document.getElementById(elmnt.id + "header").onmousedown = dragMouseDown;
  } else {
    /* otherwise, move the DIV from anywhere inside the DIV:*/
    elmnt.onmousedown = dragMouseDown;
  }

  function dragMouseDown(e) {
    e = e || window.event;
    e.preventDefault();
    // get the mouse cursor position at startup:
    pos3 = e.clientX;
    pos4 = e.clientY;
    document.onmouseup = closeDragElement;
    // call a function whenever the cursor moves:
    document.onmousemove = elementDrag;
  }

  function elementDrag(e) {
    e = e || window.event;
    e.preventDefault();
    // calculate the new cursor position:
    pos1 = pos3 - e.clientX;
    pos2 = pos4 - e.clientY;
    pos3 = e.clientX;
    pos4 = e.clientY;
    // set the element's new position:
    elmnt.style.top = (elmnt.offsetTop - pos2) + "px";
    elmnt.style.left = (elmnt.offsetLeft - pos1) + "px";
  }

  function closeDragElement() {
    /* stop moving when mouse button is released:*/
    document.onmouseup = null;
    document.onmousemove = null;
  }
}

#mydiv {
    position: absolute;
    z-index: 9;
    background-color: #f1f1f1;
    text-align: center;
    border: 1px solid #d3d3d3;
}

#mydivheader {
    padding: 10px;
    cursor: move;
    z-index: 10;
    background-color: #2196F3;
    color: #fff;
}

<!DOCTYPE html>
<html>

<body>

<h1>Draggable DIV Element</h1>

<p>Click and hold the mouse button down while moving the DIV element</p>

<div id="mydiv">
  <div id="mydivheader">Click here to move</div>
  <p>Move</p>
  <p>this</p>
  <p>DIV</p>
</div>


</body>
</html>