SO: what does this js mean? I am studying SO source code [closed]

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(some code)(jQuery);

What does this mean?

(function (a) {
    function d(g) {
        return typeof g == "object" ? g : {
            top: g,
            left: g
        }
    }
    var b = a.scrollTo = function (g, e, f) {
        a(window).scrollTo(g, e, f)
    };
    b.defaults = {
        axis: "xy",
        duration: parseFloat(a.fn.jquery) >= 1.3 ? 0 : 1
    };
    b.window = function () {
        return a(window)._scrollable()
    };
    a.fn._scrollable = function () {
        return this.map(function () {
            if (!(!this.nodeName || a.inArray(this.nodeName.toLowerCase(), ["iframe", "#document", "html", "body"]) != -1)) return this;
            var g = (this.contentWindow || this).document || this.ownerDocument || this;
            return a.browser.safari || g.compatMode == "BackCompat" ? g.body : g.documentElement
        })
    };
    a.fn.scrollTo = function (g, e, f) {
        if (typeof e == "object") {
            f = e;
            e = 0
        }
        if (typeof f == "function") f = {
            onAfter: f
        };
        if (g == "max") g = 9E9;
        f = a.extend({}, b.defaults, f);
        e = e || f.speed || f.duration;
        f.queue = f.queue && f.axis.length > 1;
        if (f.queue) e /= 2;
        f.offset = d(f.offset);
        f.over = d(f.over);
        return this._scrollable().each(function () {
            function k(w) {
                j.animate(r, e, f.easing, w &&
                function () {
                    w.call(this, g, f)
                })
            }
            var h = this,
                j = a(h),
                i = g,
                m, r = {},
                u = j.is("html,body");
            switch (typeof i) {
            case "number":
            case "string":
                if (/^([+-]=)?\d+(\.\d+)?(px|%)?$/.test(i)) {
                    i =
                    d(i);
                    break
                }
                i = a(i, this);
            case "object":
                if (i.is || i.style) m = (i = a(i)).offset()
            }
            a.each(f.axis.split(""), function (w, v) {
                var q = v == "x" ? "Left" : "Top",
                    s = q.toLowerCase(),
                    y = "scroll" + q,
                    D = h[y],
                    H = b.max(h, v);
                if (m) {
                    r[y] = m[s] + (u ? 0 : D - j.offset()[s]);
                    if (f.margin) {
                        r[y] -= parseInt(i.css("margin" + q)) || 0;
                        r[y] -= parseInt(开发者_运维问答i.css("border" + q + "Width")) || 0
                    }
                    r[y] += f.offset[s] || 0;
                    if (f.over[s]) r[y] += i[v == "x" ? "width" : "height"]() * f.over[s]
                } else {
                    q = i[s];
                    r[y] = q.slice && q.slice(-1) == "%" ? parseFloat(q) / 100 * H : q
                }
                if (/^\d+$/.test(r[y])) r[y] = r[y] <= 0 ? 0 : Math.min(r[y], H);
                if (!w && f.queue) {
                    D != r[y] && k(f.onAfterFirst);
                    delete r[y]
                }
            });
            k(f.onAfter)
        }).end()
    };
    b.max = function (g, e) {
        var f = e == "x" ? "Width" : "Height",
            k = "scroll" + f;
        if (!a(g).is("html,body")) return g[k] - a(g)[f.toLowerCase()]();
        f = "client" + f;
        var h = g.ownerDocument.documentElement,
            j = g.ownerDocument.body;
        return Math.max(h[k], j[k]) - Math.min(h[f], j[f])
    }
})(jQuery);

---

It is a closure.

It is a part of your code that can have own variables that will not be shared with the rest of your code.

And the final parenthesis have the parameters passed to this closure.

Like this:

(function (what, howmany){
    for (var i = howmany; i--;){
        alert(what);
    }
})("John",3);

In your example the closure is being calling with jquery object as parameter.

With this you can isolate the execution of this part of your code. It is powerful and must be well know to programming real javascript.

To view more information about closures in javascript see this: http://jibbering.com/faq/notes/closures/