检查错误，我给的输入是一个字符串，我想输出一个字母数。字符串中有多少个时间字母？
<!DOCTYPE html>
<html>
<head>
<title></title>
<script type="text/javascript">
function my() {
var st = document.getElementById("j").value;
var s = "l";
var letter_Count = 0;
for (var position = 0; position < st.length; position++) {
if (st.charAt(position) == s) {
letter_Count += 1;
}
}
document.getElementById("demo").innerHTML = letter_Count;
}
</script>
</head>
<body>
<p id="demo"></p>
<input type="text" name="j" id="j" onkeyup="my()" />
</body>
</html>
你忘了 "" 在 s. 这应该可以
function my() {
var st = document.getElementById("j").value;
var s = "l";
var letter_Count = 0;
for (var position = 0; position < st.length; position++) {
if (st.charAt(position) == "s") {
letter_Count += 1;
}
}
document.getElementById("demo").innerHTML = letter_Count;
}<p id="demo"></p>
<input type="text" name="j" id="j" onkeyup="my()" />