how do i make this javascript logic + syntax (very simple)

Question

Why I am getting true all the time?

var _template_id = "";
if (_template_id != '0' || _template_id!="")  {
        alert("true")
}else{
    alert("false")
}

or even if i set _template_id="0", it still turns out as true...

Answer 1

Because you're asking if _template_id isn't equal to "0" OR isn't equal to "". One of those will always be true.

Proof: Given your statement of (_template_id != '0' || _template_id!=""), let's suppose that the first part is false. Therefore _template_id == '0' is true, and hence _template_id != "" is true, so overall the statement evaluates to true.

If, on the other hand, the first part is true, then clearly the whole thing evaluates to true again.

Therefore, the statement is always true.

Answer 2

You want && not ||.

It must always be true because "0" != "", so one or the other is always true.