If you are testing your javascript based web app in older browsers of Chrome ( may be in Safari, IE) you will face this issue. When you use blur event in the DOM, general assumption is that event will be fire exactly once when the input field is foccused out either by ‘tab’ or ‘mouse click’. But in a very special scenario, i.e when the Alt+Tab is pressed, the same blur event will be fired twice.

The reason for firing twice is

1. One event fired when the field is focussed out
2. Another event fires when Window focusses

The problem is the 2nd event, which cascades the window’s blur event to all the input fields in the form.

Below code snippet will help you write the blur callback work only once per even when the Alt+Tab is pressed.

	
	/* variable to track what kind of blur event is fired */
	var _isWindowBlurEvent = false;
	
	window.onblur = function(e)
	{
		_isWindowBlurEvent = true;
	}
	
	window.onfocus = function(e)
	{
		_isWindowBlurEvent = false;
	}
	
	element.onblur = function(e)
	{
		if(! _isWindowBlurEvent ) //if the event is Element.onBlur 
		{
			/* perform your logic here*/
		}
	}
	

Test it yourself.