How to find the specific word in given paragram using javascript?

Html  Page:

<button onclick="myFunction()">Try it</button>

<p id="demo"></p>

Javascript Page:

<script>

function myFunction()

{

    var str = "Hello world, welcome to the universe.";

    var n = str.indexOf("welcome");

    document.getElementById("demo").innerHTML = n;

}

</script>

Output:

13