- Using the jQuery factory method (dollar sign function) with a selector doesn't in itself return an error; but, if it found matching elements on the page, it will return an array-like collection of nodes, which support the "length" property, just like arrays. Example, to count the number of paragraphs:
var numberOfPara = $("p").length;
if( numberOfPara == 0 )
alert("No paragraph found in this HTML document...");
else
alert("jQuery found "+ numberOfPara +" paragraphs on this page!"); - JavaScript conditional statements (like "if()") evaluate a positive number as true, and zero / negative numbers as false. Use this to quickly check if one or more elements exist on the page:
if( $("#someDiv").length ) // true if equal to 1
alert("The element 'someDiv' exists!"); - To check if the element exists and is visible, use the ":visible" pseudo-selector:
if( $("#someDiv").length && $("#someDiv:visible").length )
alert("The element 'someDiv' exists, and it is visible!");Tip: see this tutorial to check where the element is (above / below the fold, out of sight...)
- To explicitly test if the element exists but is hidden, use the ":hidden" pseudo-selector instead:
if( $("#someDiv").length && $("#someDiv:hidden").length )
alert("The element 'someDiv' exists, but it is hidden!"); - Perform these tests when the document is ready (once the full DOM has loaded, even if the onload event has not yet fired), or at least half-a-second after you've added them programmatically:
$(function(){
// The document is now ready...
});
Email AOL Mail Gmail Hotmail Yahoo Mail MS Office Excel 2010 OneNote 2010 Outlook 2010 Word 2010 OS & Devices Kindle Fire Windows 7 Web Dev C# and .NET JavaScript jQuery