js条件：如果不是false，null或undefined，则

Question

I have this !! markup for anther object and it works, but here it doesn't (in one case, works in other cases).

if (!!slides) {
        console.log("close view clear slides")
        clearInterval(slides);
    }

In firebug I get this error:

ReferenceError: slides is not defined

What should my conditional be?

Answer 1

You can't use a variable if it's not defined.

typeof(asdf)
"undefined"

!asdf
ReferenceError: asdf is not defined

if (typeof(asdf) != "undefined") {
    // will only execute if asfd is defined.
}

Answer 2

Change

if (!!slides) {

to

if (!slides) {

Though, if slides is false, null, or undefined, then clearing it wouldn't do anything. So, maybe what you mean is

if (slides) {

?