diff --git a/src/factories/createLogFilter.js b/src/factories/createLogFilter.js
index ea826cb..13ac2f8 100644
--- a/src/factories/createLogFilter.js
+++ b/src/factories/createLogFilter.js
@@ -18,17 +18,23 @@ export default (configuration: LogFilterConfigurationType) => {
   let buffer = [];
 
   const filterLog = (line: string) => {
+    
+    const subject = JSON.parse(line);
+    let isSubject = configuration.filterFunction(subject)
+    
+    if(isSubject && !(isSubject===true || isSubject===false)){
+      line = JSON.stringify(isSubject); 
+    }
+    
     buffer.push(line);
-
+    
     buffer = buffer.slice(-1 * configuration.lag - 1);
 
-    const subject = JSON.parse(line);
-
     let result;
 
     if (
       configuration.filterExpression && matchObject(subject, configuration.filterExpression) ||
-      configuration.filterFunction && configuration.filterFunction(subject)
+      configuration.filterFunction && isSubject
     ) {
       result = buffer.slice(-1 * lastLinePrinterLinesAgo - 1, -1).join('\n') + '\n' + line.trim();