To get the first index of an occurrence of the specified value in a string, use the JavaScript indexOf() method.
Example
You can try to run the following code to get the first index −
<html>
<head>
<title>JavaScript String indexOf() Method</title>
</head>
<body>
<script>
var str = new String( "Learning is fun! Learning is sharing!" );
var index = str.indexOf( "Learning" );
document.write("First index of string Learning :" + index );
</script>
</body>
</html>