var slides = $(.promo-slide);
slides.each(function(key, value){
if (key == 1) {
this.addClass(first);
}
});
Why do I get an error saying:
Uncaught TypeError: Object #<HTMLDivElement> has no method 'addClass'
From the above code?
Inside jQuery callback functions, this (and also value, in your example) refers to a DOM object, not a jQuery object.
var slides = $(".promo-slide");
slides.each(function(key, value){
if (key == 0) { // NOTE: the key will start to count from 0, not 1!
$(this).addClass("first"); // Or $(value).addClass("first");
//------^^----^
}
});
BUT: In your case, this is easier:
$(".promo-slide:first").addClass("first");
And when all .promo-slide elements in the same container, a solution in pure CSS is even easier:
.promo-slide:first-child {
/* ... */
}
As an aside, I find it a useful convention to prefix variables that contain a jQuery object with a $:
var $slides = $(".promo-slide");
$slides.each( /* ... */ );
