JavaScript error: “val.match is not a function”

I would say that val is not a string.

I get the

val.match is not function

error for the following

var val=12; 
if(val.match(/^s+$/) || val == ""){
   document.write("success: " + val);
}

The error goes away if you explicitly convert to a string String(val)

var val=12; 
if(String(val).match(/^s+$/) || val == ""){
   document.write("success: " + val);
}

And if you do use a string you don’t need to do the conversion

var val="sss"; 
if(val.match(/^s+$/) || val == ""){
   document.write("success: " + val);
}