先看动图如下，我们就可以很清楚的知道获取input标签中光标的索引的意思了。
由于IE支持document.selection，Firefox，Chrome,Safari以及Opera都有selectionStart和selectionEnd属性
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<title></title>
<link rel="stylesheet" href="">
</head>
<body>
<script>
function getTxt1CursorPosition(){
var oTxt1 = document.getElementById("txt1");
var cursurPosition=-1;
if(oTxt1.selectionStart){//非IE浏览器
cursurPosition= oTxt1.selectionStart;
}else{//IE
var range = document.selection.createRange();
range.moveStart("character",-oTxt1.value.length);
cursurPosition=range.text.length;
}
alert(cursurPosition);
}
</script>
<input type="text" id="txt1" value="abcde" onclick="getTxt1CursorPosition()">
</body>
</html>