jQuery handling undefined array value

Question

I'm looking up array values to navigate a slider back and forth and have come accross a hole in my logic regarding undefined values. As it stands, I look up the current slide within the array, add or subtract from the position in the array, and if that value exists update the position. It works, however, if the value within the array doesnt exist (i.e. there are 3 objects in the array and the sliders trying to look up #4) it throws a type error.

Need a better way of saying "if value exists, then update). Seems pretty simple but I havn't thought of a good solution.

I suppose I can easily get rid of the update variable, but I think it's good to look up the value in the array once and save it for use in the body class update, know what I mean?

See code below and thank you!

function slide(direction){

/* Get Current */

    var current = $bod.attr('class'),
        next,
        update;

/* Navigate */

    if (direction === 'right'){

        next = $current + 1;

    } else if (direction === 'left'){

        next = $current - 1;

    } else if (direction === 'home'){

        next = $home;
    }

/* Update */

    // Issue is here. If the next slide is undefined, everything crashes

    update = $slides[next].slide;

    // Was trying to address the issue with this line:

    if (update){

        $bod.removeClass(current).addClass(update);

        $current = next;
    }
}

Ricardo Lohmann · Accepted Answer · 2013-01-16 20:23:26Z

1

Try the following.

update = $slides[next] ? $slides[next].slide : false;

answered Jan 16, 2013 at 20:23

Ricardo Lohmann

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2 Comments

technopeasant Over a year ago

perfectly simple, thank you. i've never used the ? operator; mind explaining?

Ricardo Lohmann Over a year ago

@technopeasant It's called conditional operator. developer.mozilla.org/en-US/docs/JavaScript/Guide/…

Alexander · Accepted Answer · 2013-01-16 20:25:10Z

1

You should check for bounds instead.

if ((direction === 'right') && ($current < $slides.length - 1)){
  next = $current + 1;
} else if ((direction === 'left') && ($current > 0)){
  next = $current - 1;
} else if (direction === 'home'){
  next = $home;
}

answered Jan 16, 2013 at 20:25

Alexander

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