Not Able To Find the "replaceAll" Function

Not Able To Find the "replaceAll" Function

I have a function where I am trying to replace a series of "tags" with values from various forms to create a status string.  However, when I attempt to call the <string>.replaceAll() function, I get an error message that says "Not able to find "replaceAll" function".

I've tried this with a couple of other methods, such as replace() and replaceFirst() and ge tthe same error.  Additionally, I've tried calling it like this:
    <mainstring>.replaceAll("tag", "value", false);
As well as like this:
      replaceAll(mainstring, "tag", "value";

And the result is always the same.  Any ideas what is going on?