效果：
代码：
<!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>简单文本编辑器</title>
<style type="text/css">
* {
margin: 0;
padding: 0;
}
html,
body {
100%;
height: 100%;
margin: 0;
padding: 0;
font: 12px/1.5 tahoma, arial, 'hiragino sans gb', 'microsoft yahei', sans-serif;
-webkit-font-smoothing: antialiased;
overflow: hidden;
}
#mian {
640px;
height: 100%;
}
#leftBox {
background: #ecf0f5;
35px;
height: 100%;
text-align: left;
float: left;
}
#test {
border: 1px solid #eaeaea;
outline: none;
600px;
height: 100%;
resize: none;
background: rgb(250, 250, 250);
line-height: 24px;
font-size: 14px;
float: left;
padding: 10px 8px;
color: black;
font-family: inherit;
box-sizing: border-box;
}
#leftNum {
height: 100%;
100%;
resize: none;
outline: none;
overflow-y: hidden;
overflow-x: hidden;
border: 0;
background: rgb(247, 247, 247);
color: #999;
line-height: 24px;
font-size: 14px;
padding: 10px 4px;
text-align: right;
font-weight: bold;
box-sizing: border-box;
}
</style>
</head>
<body>
<div id="mian">
<div id="leftBox"><textarea wrap="off" cols="2" id="leftNum" disabled></textarea>
</div>
<textarea id="test" name="content" onkeyup="keyUp()"
onscroll="getId('leftNum').scrollTop = this.scrollTop;"></textarea>
</div>
<script type="text/javascript">
var num = "";
var test = getId('test');
function getId(obj) {
return document.getElementById(obj);
}
function keyUp() {
var str = test.value;
str = str.replace(/
/gi, ""); //
匹配一个回车符
str = str.split("
");
n = str.length;
line(n);
}
function line(n) {
var lineobj = getId("leftNum");
for (var i = 1; i <= n; i++) {
if (document.all) {
num += i + "
";// 判断浏览器是否是IE
匹配一个换行符
} else {
num += i + "
";
}
}
lineobj.value = num;
num = "";
}
</script>
</body>
</html>