I used this line in my jQuery plugin.But i didn't understand what does this line do.Below is that plugin code.

Kindly explain me briefly.

(function ($) {
    $.simpleSlideShow = function (selector, settings) {
        // settings
        var config = {
            'delay': 2000,
            'fadeSpeed': 500
        };
        if (settings) { $.extend(config, settings); }

        // variables
        var obj = $(selector);
        var img = obj.children('img');
        var count = img.length;
        var i = 0;

        // show first image
        img.eq(0).show();

        // run slideshow
        setInterval(function () {
            img.eq(i).fadeOut(config.fadeSpeed);
            i = (i + 1 == count) ? 0 : i + 1;
            img.eq(i).fadeIn(config.fadeSpeed);
        }, config.delay);

        return this;
    };
})(jQuery);

I used this line in my jQuery plugin.But i didn't understand what does this line do.Below is that plugin code.

Kindly explain me briefly.

(function ($) {
    $.simpleSlideShow = function (selector, settings) {
        // settings
        var config = {
            'delay': 2000,
            'fadeSpeed': 500
        };
        if (settings) { $.extend(config, settings); }

        // variables
        var obj = $(selector);
        var img = obj.children('img');
        var count = img.length;
        var i = 0;

        // show first image
        img.eq(0).show();

        // run slideshow
        setInterval(function () {
            img.eq(i).fadeOut(config.fadeSpeed);
            i = (i + 1 == count) ? 0 : i + 1;
            img.eq(i).fadeIn(config.fadeSpeed);
        }, config.delay);

        return this;
    };
})(jQuery);

• javascript
• jquery

• It is more mon to write this as i++; if(i===count) i=0;, or i=(i+1) % count;. The first option is simple, and the second one is somewhat idiomatic. – Kobi Commented Aug 25, 2014 at 7:31

5 Answers 5

This is simple Conditional (ternary) Operator which is same as

if(i + 1 == count){
   i = 0;
}
else{
   i = i+1;
}

Just a suggestion it could be just

i = (i+1) % count;

in English, it means: if i+1 is equal to count, then i=0. Else, i = i+1.

It's a shorthand notation in a lot of languages.

The a ? b : c syntax is a ternary operator. This will be the same as

if(i + 1 == count)
   i = 0;

else
   i = i + 1;

See more information here: https://developer.mozilla/en-US/docs/Web/JavaScript/Reference/Operators/Conditional_Operator

This is simple ternary operator as guys said already, but I would use this instead: i = ++i % count.

This is short form of if and else. Meaning of this statement

i = (i + 1 == count) ? 0 : i + 1;

is same as

if (i + 1 == count) {
   i = 0;
} else {
   i = i+1;
}