js实现拖动div

实现拖动div的基本思路

通过监听鼠标事件（mousedown、mousemove、mouseup）来实现div的拖动效果。需要记录鼠标按下时的初始位置和div的初始位置，计算移动距离并更新div的位置。

HTML结构准备

创建一个可拖动的div元素，并为其添加必要的样式：

<div id="draggable" style="width: 100px; height: 100px; background: red; position: absolute;"></div>

JavaScript实现

const draggable = document.getElementById('draggable');
let isDragging = false;
let offsetX, offsetY;

draggable.addEventListener('mousedown', (e) => {
    isDragging = true;
    offsetX = e.clientX - draggable.offsetLeft;
    offsetY = e.clientY - draggable.offsetTop;
});

document.addEventListener('mousemove', (e) => {
    if (!isDragging) return;
    draggable.style.left = `${e.clientX - offsetX}px`;
    draggable.style.top = `${e.clientY - offsetY}px`;
});

document.addEventListener('mouseup', () => {
    isDragging = false;
});

优化拖动体验

为防止拖动时选中文本，可以添加CSS样式：

#draggable {
    user-select: none;
    cursor: grab;
}

处理边界情况

确保拖动不会超出视口边界：

document.addEventListener('mousemove', (e) => {
    if (!isDragging) return;

    let left = e.clientX - offsetX;
    let top = e.clientY - offsetY;

    // 限制在视口内
    left = Math.max(0, Math.min(left, window.innerWidth - draggable.offsetWidth));
    top = Math.max(0, Math.min(top, window.innerHeight - draggable.offsetHeight));

    draggable.style.left = `${left}px`;
    draggable.style.top = `${top}px`;
});

封装为可复用函数

将拖动功能封装为可复用的函数：

function makeDraggable(element) {
    let isDragging = false;
    let offsetX, offsetY;

    element.addEventListener('mousedown', (e) => {
        isDragging = true;
        offsetX = e.clientX - element.offsetLeft;
        offsetY = e.clientY - element.offsetTop;
    });

    document.addEventListener('mousemove', (e) => {
        if (!isDragging) return;
        element.style.left = `${e.clientX - offsetX}px`;
        element.style.top = `${e.clientY - offsetY}px`;
    });

    document.addEventListener('mouseup', () => {
        isDragging = false;
    });
}

// 使用
makeDraggable(document.getElementById('draggable'));

支持触摸设备

添加触摸事件支持：

function makeDraggable(element) {
    let isDragging = false;
    let offsetX, offsetY;

    const startDrag = (clientX, clientY) => {
        isDragging = true;
        offsetX = clientX - element.offsetLeft;
        offsetY = clientY - element.offsetTop;
    };

    const drag = (clientX, clientY) => {
        if (!isDragging) return;
        element.style.left = `${clientX - offsetX}px`;
        element.style.top = `${clientY - offsetY}px`;
    };

    const endDrag = () => {
        isDragging = false;
    };

    // 鼠标事件
    element.addEventListener('mousedown', (e) => startDrag(e.clientX, e.clientY));
    document.addEventListener('mousemove', (e) => drag(e.clientX, e.clientY));
    document.addEventListener('mouseup', endDrag);

    // 触摸事件
    element.addEventListener('touchstart', (e) => {
        e.preventDefault();
        startDrag(e.touches[0].clientX, e.touches[0].clientY);
    });
    document.addEventListener('touchmove', (e) => {
        e.preventDefault();
        drag(e.touches[0].clientX, e.touches[0].clientY);
    });
    document.addEventListener('touchend', endDrag);
}