On change of caller field on incident form show UI Macro ?

[Tejasr1]

I have done Servicenow to Whatspp integration :

I have randomly chosen the Use case : I have created a UI macro and placed  beside the caller field of incident form.When anyone click on whatspp icon it redirect to selected  caller whatspp and send a incident details to him/her.
But I want to show whatspp icon on change of caller field.
Below is my code.
Can someone Please help me?

<?xml version="1.0" encoding="utf-8" ?>
<j:jelly trim="false" xmlns:j="jelly:core" xmlns:g="glide" xmlns:j2="null" xmlns:g2="null">
<a><img src="whatsppicon.png" width="70%" height="70%" onclick="whatsppWindow('${ref}')"></img></a>
<script>
function whatsppWindow(reference)//incident.caller_id
{
 var demotext;
 var mob;
 var incSysid = g_form.getUniqueValue();
 alert(incSysid);
 var refVal= reference.split('.');
 var fieldName=refVal[1];
 var sysId=g_form.getValue(fieldName);//Get caller Sys_id
 var user=new GlideRecord('sys_user');
 if(user.get(sysId))
{
  mob=user.mobile_phone.toString();
}
var incident=new GlideRecord('incident');
if(incident.get(incSysid))
{
 demotext = "Hi " + user.first_name + ",\nYour Incident Number is: " + incident.number + '\nYour Issue Description is: ' + incident.short_description;
}

mob=mob.replace(/[^0-9]+/gi,'');
if(mob)
{
open('https://wa.me/'+mob+'?text='+encodeURIComponent(demotext),'_top');
}

}
</script>
</j:jelly>​

@Ankur Bawiskar

[Ankur Bawiskar · Accepted solution]

@Tejasr1 

let the icon be there always and anyhow based on what value is present in the field the same will be picked up in the UI macro

[Tejasr1]

Thanks for the Suggestion.

[Tejasr1]

@Ankur Bawiskar 
Can you suggest me more use cases on servicenow to Whatspp integration?

Regards 
Tejas

[Ankur Bawiskar]

@Tejasr1 

I haven't implemented it for any customer, so cannot share any.