JSFiddle - React, Tailwind, and code Playground

HTML

<textarea></textarea>

CSS

textarea { width:500px; height:300px; }

JavaScript

$(function() {
    var str="<TAG>~다른태그~<REG_NO>740111-1102222</REG_NO><ID>id1</ID><REG_NO>740111-1111111</REG_NO>~다른태그~<ID>    id2    id!    </ID>~다른태그~</TAG>"; 
    var res = str.replace(/(<REG_NO>\s*)(.*?)(\s*<\/REG_NO>)/g, idChangeCallback);
    
    $('textarea').val(res);
    
    function ChangeCallback($0, $1, $2, $3) {
        //alert($2);
        
        var tmp = $2;
        var aftStr = "";
        
        alert(tmp);
        for(i=0; i<tmp.length; i++){
            if( i % 2 == 1 ) {
                aftStr += tmp[i]+"!!";
            }
            else {
                aftStr += tmp[i];
            }
        }
        //if($2.len == 14) { alert($2); }
        //alert("$0 : " + $0 + "\n$1 : " + $1 + "\n $2 : " + $2 + "\n $3 : " + $3);
        
     
        return $1+aftStr+$3;
    }
});