js原生拖拽框架

模板对象.onmousedown = function(){

    console.log('按下');

    document.onmousemove = function(){
        console.log('移动');
    }

    document.onmouseup = function(){
       console.log('松开');
       //松开后，记得解绑移动事件
       document.onmousemove = null;
    }

}



           

简单的方块拖动算法一

<style>
#box{
    position: fixed;
    width: 100px;
    height: 100px;
    background-color:red;
}
</style>

<div id="box"></div>

<script>
    var box = document.getElementById('box');

    box.onmousedown = function( event ){

        var distX = event.clientX - box.offsetLeft;
        var distY = event.clientY - box.offsetTop;

        var maxLeft = window.innerWidth - box.offsetWidth;
        var maxTop = window.innerHeight - box.offsetHeight;

        document.onmousemove = function(event){
           
            var x = event.clientX - distX;
            if( x<=0 ) x = 0;
            if(x>=maxLeft) x = maxLeft;
            var y = event.clientY - distY;
            if(y<=0)y=0;
            if(y>=maxTop)y = maxTop;
            box.style.left = x + 'px';
            box.style.top = y + 'px';
        }

        document.onmouseup = function(){
            // console.log('松开');
            //松开之后清空移动事件，避免松开还能拖
            document.onmousemove = null;
        }

    }
</script>
           

简单方块拖拽算法二

<style>
#box{
    position: fixed;
    width: 100px;
    height: 100px;
    background-color:red;
}
</style>

<div id="box"></div>

<script>
    var box = document.getElementById('box');

    box.onmousedown = function( event ){

        var boxLeft = box.offsetLeft;
        var boxTop = box.offsetTop;

        var startX = event.clientX;
        var startY = event.clientY;

        var maxLeft = window.innerWidth - box.offsetWidth;
        var maxTop = window.innerHeight - box.offsetHeight;

        document.onmousemove = function(event){
           
            var endX = event.clientX;
            var endY = event.clientY;
            var distX = endX - startX;
            var distY = endY - startY;
            var left = boxLeft + distX;
            var top = boxTop + distY;

            box.style.left = left + 'px';
            box.style.top = top + 'px';

        }

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

    }
</script>
           

计算尺寸

1. window.innerWidth

   ：获取屏幕可视宽

2. window.innerHeight

   ：获取屏幕可视高

3. dom对象.offsetLeft

   ：获取对象的左偏移值

4. dom对象.offsetTop

   ：获取对象的顶偏移值

5. dom对象.offsetWidth

   ：获取对象的宽度（包含边框、填充、滚动条）

6. dom对象.offsetHeight

   ：获取对象的高度（包含边框、填充、滚动条）

7. event.clientX

   : 获取对象距屏幕左侧边缘X坐标

8. event.clientY

   : 获取对象距屏幕顶部侧边缘Y坐标

特别注意：当

display:none

时，那么使用

offsetWidth

或者

offsetHeight

取不到它的宽度和高度，返回数值0，解决方案可以使用

visibility:hidden

，这样可以获取值。

window对象

获取可视宽、可视高

window.innerHeight

，

window.innerWidth