Question

I am doing a comparison on dates in javascript. In this case date1 is empty "" and I can see the same in firebug. As per the code below, the first alert shouldn’t be called because date1 == "", but for some reason the alert alert(" This is called...."); is invoked. What is wrong here?

if(date1 != null || date1 != ""){

        if( (date1 != null || date2 != "") && (date1 < date2)){
                alert(" This is called....");
                break;
        }
        else{
            alert(" That is called....");
            break;
        }

    }

The above if condition is inside a for loop, hence the break.

Answer 1

I think you mean to be using && instead of || in your first comparision to make sure that both conditions are true and I think you have typo where you’re using date1 instead of date2 in the second test. Further, you can just use if (date1) to simultaenously rule out null and "" and undefined and 0 and NaN and any other falsey value.

I think you want something like this:

if (date1) {
    if(date2 && date1 < date2) {
        alert(" This is called....");
    } else {
        alert(" That is called....");
    }
    break;
}

If what you’re really trying to do is make sure that date1 and date2 are legal numbers, then I’d suggest you do this:

if (typeof date1 == "number") {
    if(typeof date2 == "number" && date1 < date2) {
        alert(" This is called....");
    } else {
        alert(" That is called....");
    }
    break;
}

Or, if they’re supposed to be Date objects, then you can test for that:

if (date1 instanceof Date) {
    if(date2 instanceof Date && date1 < date2) {
        alert(" This is called....");
    } else {
        alert(" That is called....");
    }
    break;
}