probable issues:

• variable is NUMBER (instead of string);
  num=35; num.replace(3,'three'); =====> ERROR
num=35; num.toString().replace(3,'three'); =====> CORRECT !!!!!!
num='35'; num.replace(3,'three'); =====> CORRECT !!!!!!
• variable is object (instead of string);
• variable is not defined;

Replace wouldn't replace numbers. It replaces strings only.

This should work.

function trim(str) {
    return str.toString().replace(/^\s+|\s+$/g,'');
}

If you only want to trim the string. You can simply use "str.trim()"

You are not passing a string otherwise it would have a replace method. I hope you didnt type function trim(str) { return var.replace(blah); } instead of return str.replace.

You should probably do some validations before you actually execute your function :

function trim(str) {
    if(typeof str !== 'string') {
        throw new Error('only string parameter supported!');
    }

    return str.replace(/^\s+|\s+$/g,'');
}

Did you call your function properly? Ie. is the thing you pass as as a parameter really a string?

Otherwise, I don't see a problem with your code - the example below works as expected

function trim(str) {
    return str.replace(/^\s+|\s+$/g,'');
}


trim('    hello   ');  // --> 'hello'

However, if you call your functoin with something non-string, you will indeed get the error above:

trim({});  // --> TypeError: str.replace is not a function

In case of a number you can try to convert to string:

var stringValue = str.toString();
return stringValue.replace(/^\s+|\s+$/g,'');

You should use toString() Method of java script for the convert into string before because replace method is a string function.

I fixed the problem.... sorry I should have put the code on how I was calling it too.... realized I accidentally was passing the object of the form field itself rather than it's value.

Thanks for your responses anyway. :)

make sure you are passing string to "replace" method. Had same issue and solved it by passing string. You can also make it to string using toString() method.