spin.js

$.extend(KhanUtil, {
    spin: function(content) {
        // First find all top-level blocks and spin them
        var startingBracePos = -1;
        var nestingLevel = 0;

        for (var i = 0; i < content.length; i++) {
            if (content.charAt(i) === "{") {

                // We encounter our first "{"
                if (startingBracePos === -1) {
                    startingBracePos = i;

                // We are already inside a top-level block, this starts a nested block
                } else {
                    nestingLevel++;
                }

            // We encounter a "}" and have seen a "{" before
            } else if (content.charAt(i) === "}" && startingBracePos !== -1) {

                // This is the closing brace for a top-level block
                if (nestingLevel === 0) {
                    // Spin the top-level block
                    var spun = KhanUtil.spin(content.substring(startingBracePos + 1, i));
                    content = content.substring(0, startingBracePos) + spun + content.substring(i + 1);
                    i -= (i - startingBracePos) - spun.length + 1;
                    startingBracePos = -1;

                // This brace closes a nested block
                } else {
                    nestingLevel--;
                }
            }
        }

        return KhanUtil.randFromArray(content.split("|"));
    }
});


$.fn.spin = function() {
    this.find(".spin").each(function() {
        var spun = KhanUtil.spin($(this).html());
        $(this).html(spun);
    });
};