JavaScript使用indexOf查找子字符串位置

<!DOCTYPE html>
<html>
<body>
<p id="demo">
Click the button to locate where in the string
a specifed value occurs.</p>
<button onclick="myFunction()">Try it</button>
<script>
function myFunction()
{
var str="Hello world, welcome to the universe.";
var n=str.indexOf("welcome");
document.getElementById("demo").innerHTML=n;
}
</script>
</body>
</html>