How to check if an eval name is undefined

I can think of three solutions:

1. You can make an assumption that empty m1/m2 means 0, so there will never be an undefined value. This really simplifies things.
2. You can use regexp to check first for any occurrence of m1 or m2 in the equation and if it exists then check if is undefined.
3. But the best method is to use try...catch.

Try/Catch Example:

try {
    eval('12+3+m1');
} catch (e) {
    alert(e.message);
}