jquery to determine if the child element of the element exists in the sample code _jquery

jquery Determines whether child elements exist

first, to determine whether child elements exist
First-level child element if ($ ("#specialId >img"). Length==0)
if ($ ("#specialId: Has (IMG)"). Length==0)
{
-----does not have an IMG child tag-----
}
Else
{
-------has an IMG child tag------
}

Select specific ID child elements under a specific ID element
$ ("#form"). Children ("#t") so

Third, select a child element under a specific ID element
$ ("Ul#u>li:nth-child (2)") so

Iv. Determining whether an element exists
if ($ ("#myId"). length>0)
{
Exist
}