JSFiddle - React, Tailwind, and code Playground
HTML
<textarea rows="4" cols="50">
+447222555555
0800 042 0213
2017/07/14
2017/07/17
2017/07/27
</textarea>
<button onclick="myFunction()">Click me</button>
JavaScript
function myfunction() {
onclick=`(((\+44\s?\d{4}|\(?0\d{4}\)?)\s?\d{3}\s?\d{3})|((\+44\s?\d{3}|\(?0\d{3}\)?)\s?\d{3}\s?\d{4})|((\+44\s?\d{2}|\(?0\d{2}\)?)\s?\d{4}\s?\d{4}))(\s?\#(\d{4}|\d{3}))?`
}