javascript - 如何为多个元素分配拖动功能/监听器？

Question

我正在创建一个包含多个可拖动 div 的页面，并且正在寻找一种方法来优化我的代码。

我知道如何将这个 JS 应用到每个 id 的唯一方法是复制和粘贴整个 JS 代码块 4 次并更改 id 但我知道必须有更有效的方法，但是，我不是对 JS 非常熟悉。

我最初的想法是做这样的事情

dragElement(document.getElementById("draggable", "draggable2", "draggable3", "draggable4"));

但它不起作用。我怎样才能以更有效的方式实现我想要的目标？

这是我的代码

<div id="draggable"><div id="draggableimg"></div></div>
<div id="draggable2"><div id="draggable2img"></div></div>
<div id="draggable3"><div id="draggable3img"></div></div>
<div id="draggable4"><div id="draggable4img"></div></div>

JS

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

function dragMouseDown(e) {
    e = e || window.event;
    e.preventDefault();
    _curDragEle = this;
    // 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) {
    _curDragEle.classList.remove("dragstart")
    _curDragEle.className = _curDragEle.className + " dragstart";
  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() {
    var k = document.querySelectorAll(".dragstart")
    for(var i=0; i < k.length;i++){
        k[0].classList.remove("dragstart")
    }
    /* stop moving when mouse button is released:*/
    document.onmouseup = null;
    document.onmousemove = null;
  }
}

Answer 1

忘记 id，它们会导致您正面临的问题类型。相反，给所有可拖动元素一个公共(public)类。然后收集所有元素并循环遍历它们。

// Gather all the draggable elements up into a collection
let draggables = document.querySelectorAll(".draggable");

// Loop over the collection
draggables.forEach(function(el){
  dragElement(el);
});

function dragElement(el){
  console.log(el + " is now draggable!")
}

<div class="draggable"><div id="draggableimg"></div></div>
<div class="draggable"><div id="draggable2img"></div></div>
<div class="draggable"><div id="draggable3img"></div></div>
<div class="draggable"><div id="draggable4img"></div></div>