如何才能仅执行一次ajax调用？

我正在加载facebook likebox滚动，但是每次我向上/向下滚动时，都会触发ajax，而我只希望ajax触发一次。这是代码：

jQuery(document).ready(function() {
    jQuery(window).scroll(function() { 
        var scroll = jQuery(window).scrollTop();

        if (scroll <= 770) {
      jQuery.get('ajax/facebook.html', function(data) { jQuery('.fblikeajax').html(data);});
        }

    }); 
}); 

Unbind the event listener after it fires:

jQuery(document).ready(function() {
    var scrollHandler = function() { 
        var scroll = jQuery(window).scrollTop();

        if (scroll <= 770) {
      jQuery.get('ajax/facebook.html', function(data) { jQuery('.fblikeajax').html(data);});
        }
        $(window).unbind('scroll', scrollHandler);
    }
    jQuery(window).scroll(scrollHandler); 
}); 

I haven't tested that code, but it should be pretty close.

You could add in a variable that checks if the ajax has been fired:

jQuery(document).ready(function() {
    var ajax_fired = false;
    jQuery(window).scroll(function() { 
        var scroll = jQuery(window).scrollTop();

        if ((scroll <= 770) && !ajax_fired) {
            ajax_fired = true;
            jQuery.get('ajax/facebook.html', function(data) {
                jQuery('.fblikeajax').html(data);

            });
        }

    }); 
}); 

Use JQuery's on() and off()

$(document).on("scroll", scrollcheck);

var scrollcheck = function () {
    var scroll = jQuery(window).scrollTop();
    if (scroll <= 770) {
        jQuery.get('ajax/facebook.html', function (data) {
            jQuery('.fblikeajax').html(data);
        });
        $(document).off("scroll", scrollcheck);
    }
}