Execute function if document is taller than viewport

问题

This is some quite strange behaviour I experience. I want to execute a function only when the document is taller than the viewport (i.e. it overflows it and a scrollbar appears). I use this code:

var docH = $("document").height(),
    viewPortH = $("window").height();

if (docH > viewPortH) {
 // execute functions
}

But nothing happens and console returns:

Uncaught TypeError: Cannot read property 'parent' of null

Does anyone know what the problem is/what code I should use to see whether the document is taller than the viewport?

回答1:

document and window are objects not selectors.

var docH = $(document).height(),
    viewPortH = $(window).height();

回答2:

You don't need the quotes around document and window.

var docH = $(document).height(),
    viewPortH = $(window).height();

if (docH > viewPortH) {
 // execute functions
}

Example fiddle

With the quotes in place jQuery was actually looking for elements like <document /> and <window /> in the DOM.

回答3:

try using document and window like this: var docH = $(document).height(), viewPortH = $(window).height();

来源：https://stackoverflow.com/questions/14231568/execute-function-if-document-is-taller-than-viewport