regex - Javascript mark substrings onchange event -

i trying highlight substrings of large string. following code highlights if substring first letter of large string. how can fix this? in advance

 function search() {         var text = document.getelementbyid("searchtext").value;          if (!text) return;          var regex =  new regexp(text, 'gi');         var str = document.getelementbyid("input").innerhtml;         var n=str.match(regex);              document.getelementbyid("input").innerhtml = document.getelementbyid("input").innerhtml.replace(str, '<span style="background-color:clear;">'+str+'</span>'); // clear              document.getelementbyid("input").innerhtml = document.getelementbyid("input").innerhtml.replace(n, '<span style="background-color:yellow;">'+n+'</span>');       } 

try this:-

demo

function search() {     var hid = document.getelementbyid('hidtxt').value;     if(hid.length == 0) hid.value=document.getelementbyid("input").innerhtml;         var text = document.getelementbyid("searchtext").value;        if (!text) return;         var regex =  new regexp(text, 'gi');             document.getelementbyid("input").innerhtml = hid.replace(regex, '<span style="background-color:yellow;">$&</span>');       }