Check block existence by jQuery

How do I know if there is a block with class "media" on the page?

if(<div 开发者_JS百科class="media"></div> exist in current page){
//then do something
}

This code doesn't work:

if($(".media")){ //do }

You need to check if ($('.media').length).

$(...) returns a jQuery object, which will always be "truthy", even when empty.
However, if it's empty, its length property will be 0, which is "falsy".

You can also be more explicit and write if ($('.media').length > 0).

You can use .length to check for existance

   if ($(".media").length)
    {//do something}

if ($(".media").length > 0) { ... }

if($(".media").length){ //do }

One way to do it is:

if ($("div.media").length > 0) {
    // Then do something.
}

Hint: use the tag name div before the class .media because it is more efficient.