stop event after first time

Question

i am firing an event when im at a special scrollposition with jquery.inview . it works by adding classes if an element is in the viewport. in my script im saying the following

    var $BG = $('#BG')
$('#BG').bind('inview', function (event, visible) 
{
        if (visible == true) {
        $(this).addClass("inview");

        } else {

        $(this).removeClass("inview");
        }
    });

   if($BG.hasClass("inview")){

        $('#diagonal').css('left',0)
        $('#diagonal').css('top',0)

    }

but it fires the .css events again and again, but i want them to fire only at the first time the #BG gets the "inview" class. thanks ted

Answer 1

You can unbind the event handler using jQuery unbind method or use one method to handle event at most once.

http://api.jquery.com/category/events/event-handler-attachment/

Answer 2

You can add some var who tells if it has been fired or not :

var $BG = $('#BG'), firedInView = false;

$BG.bind('inview', function (event, visible) {
    if(!firedInView) {
        firedInView = true; //set to true and it won't be fired
        //do your stuff
    }
});

Answer 3

尝试使用.one()代替.bind() ：

$('#BG').one('inview',

Answer 4

I am going on the assumption that you would like to remove the styles on diagonal when #BG is out of view?

I'd split this into two listeners

//If bg does not have class inview, addClass if it is visible
$('body').on('inview', '#BG:not(.inview)', function (event, visible) {
    if (visible == true) {
        $(this).addClass("inview");
        $('#diagonal').css({'left': 0, 'top': 0});
    }
});

//If bg does has class inview, removeClass if it is invisible
$('body').on('inview', '#BG.inview', function (event, visible) {
    if (visible == false) {
        $(this).removeClass("inview");
        $('#diagonal').css({'left': 'auto', 'top': 'auto'});
    }
});