JavaScript

The Marp suite of tools is great for creating presentations from simple Markdown rules.

I've previously written about how to get up and running with Marp, but as I have been using it for a while I have come up with a few things that might be useful to know about if you are getting to grips with it.

Here's a list of what I'll be talking about.

1. Using HTML In Slides
2. Adding Speaker Notes
3. Using Spot Directives
4. Using Images
5. Generate A Presentation From A Document
6. Jump To A Slide
7. Creating Custom Themes

Marp or Markdown Presentation Ecosystem is a collection of tools that allows the generation of presentations of different formats from a markdown template. The tools are written in JavaScript and have a number of options that allow presentations of different styles and formats.

This tools stood out to me as it has syntax highlighting built in and allows the creation of presentations using markdown. The presentation can also be altered using standard CSS styles.

I've spent many hours fiddling with presentations in Keynote and Google Slides, so I wanted something that would be simple to use and generate the presentation files I needed.

Adding a progress bar to the top of the page is a simple way of showing the user how far down the page they have read. There is a scroll bar on the right hand side of the page on my current device, but that isn't always present on all devices. It is possible to hide the scroll bar on Macs and mobile devices so that they are only shown as the page is being scrolled.

Putting this piece of information at the top of the page can be a useful indicator that augments already existing technologies.

I was working on a user dashboard recently and decided to add some more signposting to values being updated.  Users were able to select different parameters in order to produce different values, but I thought that the values being updated weren't clear enough.

I had the idea to add some animation to the number as it was updated. This would show the user what items changed as they updated the dashboard. As the dashboard project had jQuery installed this gave me a nice animation system to use.

The HTML of the dashboard was quite simple and contained a number of div elements that contained numbers. Each of the different numbers had a id so that it could be updated independently.

When I first heard the term "Shadow DOM" I had to laugh at the name. I had visions of a cloak and dagger HTML element that would only be seen on the dark web. Or some sort of nefarious shadow site that was the after effect of a hack. In reality, this is quite a useful bit of technology that has a number of applications, although it does need a fairly modern browser to be able to use it. Shadow DOM is part of the web components strategy, which includes custom elements and HTML templates. These give developers the power to create custom tools and experiences that are encapsulated away from other parts of the code.  In this article I will go though what the shadow DOM is, how to use it, and in what situations it comes in handy.

Bar charts are powerful ways to show the relationships between different data items. If the data you want to show is discrete then a simple horizontal segmented bar chart is a good idea. You can easily change a collection of numbers into a related set of attributes.

To display this bar chart you don't need a large JavaScript library or an backend charting system, you just need a few lines of markup and some styles. Here is all of the markup needed to generate the bar chart. This consists of a wrapper element and four inner elements that make up the data of the bar chart. Note that the width of each element is pre-calculated to be 25%. I'll address the maths involved in this later in the post.

Adding events to HTML elements with jQuery is pretty simple, but I found that extending those events wasn't an easy task. I was faced with an issue where I had some third party code that performed an action on an element, and I needed to add an event and call the same handler from that event. As this was within a CMS I had limited scope to just add my new event to the existing code, so I needed a way of pulling out the current jQuery events and then calling that event handler separately. This post looks at how I accomplished this.

Let's start with a couple of simple form input elements.

<input type="text" class="field-text" />
<input type="text" class="field-next" />

As an example that can be useful here I'm going to set up a 'change' event that will copy the text entered into field-text into the field-next. This is a simple enough example and doesn't require that much code.

After looking at Conway's game of life I have been looking at other forms of cellular automata. This lead me to discover Langton's ant, which is a different kind of cellular automata where an agent (namely an ant) is used to turn the squares on or off as it travels around a grid.

The rules of Langton's ant are quite simple. The ant simply follows two rules as it moves around the grid.

Tests for programmers in an interview process are not uncommon. For the last couple of years I have asked a quick pre-interview question to junior developers to see what sort of stuff they come up with.

As I don't want to set any developer a task that will take longer than absolutely needed I opted to set a very simple task for them. Commonly known as "FizzBuzz", this task is as follows.

"Write a program that prints the numbers from 1 to 100. But for multiples of three print "Fizz" instead of the number and for the multiples of five print "Buzz". For numbers which are multiples of both three and five print "FizzBuzz"."

The expected output for this would be something like this.

To verify that an element exists in the DOM you just need to use the .length property of a jQuery lookup. If the element is there then the number of elements found will be greater than 0.

if ($('.myelement').length > 0) {
}

This can be shorted by implicitly checking for a positive value of length.

if ($('.myelement').length) {
}

This is useful if you want to check that an element doesn't exist before trying to add it to the DOM. This helps to stop duplicate elements being added, which can create issues.

if ($('.myelement').length == 0) {
}