Problem with html code in applicant front office

Hello,
I’d like to put a html code in applicant form with html code select to change the format of a phone number like 01020304 to 01-02-03-04

All works correctly with this code in front office, but the result of the html in applicants back office is sempty.

How can i fix this problem.

Yhanks

<input onkeydown="tape(this,2,'-')">
<script language='javascript'>
    var num=0;
    function tape(id,nbr,crt){
        len=id.value.length;
        mod=(len-num)%nbr;
        if(mod==0 && len!=0)
        {
            id.value=id.value+crt;
            num++;
        }
    }
</script>

https://ww.wp.xz.cn/plugins/job-manager/