<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<title>Document</title>
<style>
.box {
position: fixed;
border: 1px solid #000;
}
</style>
</head>
<body>
<script>
{
let startMouse = {};
let el;
/*
从左向右画框:
1. 记录摁下鼠标坐标 - 元素的 left
2. 移动时记录新坐标
1) 计算差值
2）差值就是元素的宽度
从右向左画框:
!!! 注意这里 left 值 应该是move时的鼠标位置
left 值应该是在 左侧的这个值，也就是两个值中的最小值
*/
let move = (e)=>{
let nowMouse = {
x: e.clientX,
y: e.clientY
};
let dis = {
x: nowMouse.x - startMouse.x,
y: nowMouse.y - startMouse.y
};
el.style.left = Math.min(startMouse.x,nowMouse.x) + "px";
el.style.top = Math.min(startMouse.y,nowMouse.y) + "px";
el.style.width = Math.abs(dis.x) + "px";
el.style.height = Math.abs(dis.y) + "px";
}
document.addEventListener("mousedown",(e)=>{
el = document.createElement("div")
startMouse = {
x: e.clientX,
y: e.clientY
}
el.className = "box";
document.body.appendChild(el);
document.addEventListener("mousemove",move);
document.addEventListener("mouseup",()=>{
document.removeEventListener("mousemove",move);
},{once:true});
e.preventDefault();
});
}
</script>
</body>
</html>
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