jquery checks the existence of elements

JavaScript checks the existence of elements:

Even if this element is deleted, there is no worry about JavaScript code error;

jquery checks the existence of elements:

The code is as follows:

if (!document.getelementbyid ("Preview")) return false;

jquery $ ("#preview") gets the object forever, even if there is no such element on the page.

You cannot use the following code:

if ($ ("#preview") {
Do something
}

So to use jquery to check if an element exists on a Web page, it should be judged based on the length of the element being fetched.

The code is as follows:

if ($ ("#preview"). Length>0) {
Do something
}

jquery checks the existence of elements