要替换JavaScript中特定索引处的字符，您可以尝试运行以下代码
<html>
<head>
<title>JavaScript Boolean</title>
</head>
<body>
<script>
var str = "cric";
document.write("Original String: "+str);
var index = 3;
str = str.substr(0, index) + 'x' + str.substr(index + 1);
document.write("<br>New String: "+str);
</script>
</body>
</html>