How do i compare against an empty variable?

Question

If I set a variable to 0, I get the weird behavior that a comparison to "" (empty) is true. How do I check that the variable is really empty?

tmp = 0;

if ( tmp != "")
{
    //do something - This is where the code goes.
}
else
{
   //isEmpty - I would expect to be here
}

Answer 1

Use strict comparison operators === and !==

With == and != (called abstract comparison operators),

If the two operands are not of the same type, JavaScript attempts to convert the operands to an appropriate type for the comparison.

---

If by empty, you want to check if the variable hasn't been defined, use:

if (typeof tmp !== "undefined") {
    // it exists!
}