Tell if  or  has focus using native Javascript
87247
Using jQuery to test if an input has focus
53203
Checking for undefined
95690
Check if JavaScript is enabled with PHP
145643
JavaScript style for optional callbacks
113905
How can I check whether a variable is defined in JavaScript?
44858
JavaScript isset() equivalent
44048
How do I know if the page is in Edit Mode from JavaScript?
55122
Read JavaScript native code
27983
How can I tell if a DOM element is visible in the current viewport?
995
CSS: :focus of elements within contenteditable
142191
Can javascript tell the difference between left and right shift key?
3002
How to focus on the selected object?
82560
Can software auto-detect image focus?
70566
How do I check if an object has a key in JavaScript?
146880
Detect if an element is visible with jQuery
27606
Detecting an undefined object property
131979
Detect enter key pressed using javascript