xxxxxxxxxx<html lang="en"><head><meta charset="utf-8"><title>Check If a String Contains a Substring in JavaScript</title></head><body> <script> // Sample string var str = "The quick brown fox jumps over the lazy dog." // Check if the substring exists inside the string var index = str.indexOf("fox"); if(index !== -1){ document.write("Substring found!"); } else{ document.write("Substring not found!"); } </script></body></html>