js determines whether an element exists on the page_javascript skills

1. Determine whether the form element exists (1)

Copy code The code is as follows:

Code highlighting produced by Actipro CodeHighlighter (freeware)http://www.CodeHighlighter.com/-->if("periodPerMonth" in document.theForm)
{
return true;
}
else{
return false;
}

2. Determine whether the page element exists

Copy code The code is as follows:

if(document.getElementById("XXX"))
{
//Exists
}

3. Determine whether the form element exists (2)

Copy code The code is as follows:

if(document.theForm.periodPerMonth)
{
//Exists
} or
if(typeof(document.theForm.periodPerMonth) == "object")
{
//Exists
}

4. Determine whether the form exists

Copy code The code is as follows:

if(document.theForm)
{
//Exists
}

5. Write a script with Jquery

Copy the code The code is as follows:

if ( $("#someID").length > 0 ) {
$("#someID").text("hi");
}