Business Rule Help needed!!

[Snow Angel]

Can someone help me fix this BR so it shows the attachment file ext.

Currently its creating (required) prefix by picking up the value from a field, and creating a new file name as prefix + hyphen + file name. But for some reason not picking up the file extension.

Requirement : The total name character limit is 100 i.e prefix + filename.ext 

Business Rule:

(function executeRule(current, previous /*null when async*/ ) {
var auditGR = new GlideRecord(current.table_name);
auditGR.get(current.table_sys_id);
if (auditGR.u_pbc_id) {
current.file_name = auditGR.u_pbc_id + " - " + current.file_name;
}
})(current, previous);

This is what it shows currently in the activity, its missing the file ext.

[Satishkumar B]

@Snow Angel please check your inbox i have texted you.

[Satishkumar B · Accepted solution]

@Snow Angel 
try this:

(function executeRule(current, previous /*null when async*/ ) {

    var auditGR = newGlideRecord(current.table_name);

    auditGR.get(current.table_sys_id);

    if (auditGR.u_pbc_id) {

        var extensionIndex = current.file_name.lastIndexOf(".");

        var extension = current.file_name.substring(extensionIndex);

        var filename = auditGR.u_pbc_id + " - " + current.file_name;

        if (filename.length > 100) {

            filename = filename.substring(0, 100 - extension.length) + extension;

        }

        current.file_name = filename;

    }

})(current, previous);

[Snow Angel]

@Satishkumar B 

u_pbc_id is a string field and its manually entered and this is the format OIG-001 (xxx-xxx)