Primitive JavaScript (BYOSP Part 7)

Tuesday, February 28, 2012

When starting into the animations I decided it was time to refactor. One problem was the little "updateState" calls floating around inside conditional logic – always a bad sign. A second problem was the sheer number of strings and CSS selectors in the code.

I've become more sensitive to primitive obsession in JavaScript. Some code I see is nothing but strings and numbers. I think the obsession hurts readability and maintainability.

The selectors scattered in the slide presenter code do one of three things: get all slides, get the next slide, and get the previous slide. It would be nice to hide all of these behind tiny function abstractions.

var slides = function () {
    return $("section");
};

var nextSlide = function () {
    return $("section.current").next("section");
};

var previousSlide = function () {
    return $("section.current").prev("section");
};

Those functions make the logic for moving around much easier to read.

var moveForward = function () {
    setCurrentSlide(nextSlide());
};

var moveBackward = function () {
    setCurrentSlide(previousSlide());
};

var moveFirst = function () {
    setCurrentSlide(slides().first());
};

var moveLast = function () {
    setCurrentSlide(slides().last());
};

As a bonus, all of the book keeping logic for setting the current slide moves into a single location.

var setCurrentSlide = function (slide) {
    if (slide.length > 0) {
        slides().removeClass("current");
        slide.addClass("current");
        updateHistory(slide);
    }
};

Having a central location to set the currently selected slides is important for the upcoming animation logic.

For all the code, see github.


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