How to automatic to create an HTML anchor tag around the string using javascript?

Html page:

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

Javascript page:

<script>

    function myFunction() {

        var txt = "Chapter 10";

        txt.anchor("chap10");

        alert(txt.anchor("chap10"));

    }

</script>

Output:

<a name="chap10">Chapter 10</a>