javascript - catch SyntaxError and run alternate function

I'm trying to build something on javascript that I can have an input that can be everything like string, xml, javascript and (non-javascript string without quotes) as follows:

//strings
    eval("'hello I am a string'"); /* note the following proper quote marks */

//xml
    eval(<p>Hello I am a XML doc</p>);

//javascript
    eval("var hello = 2+2;");

So this first 3 are working well since they are simple javascript native formats

but when I try use this inside javascript

//plain-text without quotes
    eval("hello I am a plain text without quotes");
    //--SyntaxError: missing ; before statement:--//

Obviously javascript interprets this as syntax error because it thinks its javascript throwing a SyntaxError.

So what I would like to do it to catch this error and perform the adjustment method if this occurs.

I've already tried with try catch but it doesn't work since it keeps returning the Syntax开发者_C百科 error as soon as it tries to execute the code.

Any help would be much appreciated

Cheers :)

Additional Information: Imagine an external file that javascript would read, using spidermonkey, so it's a non-browser stuff(I can't use HttpRequest, DOM, etc...)..not sure if this matters, but there it is. :)

Are you sure a Try...Catch block won't work? This example works for me in firefox.

try {
  eval("hello I am a plain text without quotes");
} catch(err) {
  alert("error caught");
}