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HTML5 Series - Error Handling

One thing you can say for certain about writing code is at some point your going to write something that error's. It may be picked up in code reviews, or by a tester, and then fixed but for certain as you are human at some point you will make a mistake. What's important though is what happens after the mistake.

If your a C# developer then good news JavaScript has the same try, catch, finally functionality that C# has and it works in the same way.

Wrap you code that could error with a try statement and curly braces and following it add in a catch statement with the code that you want to execute in the event of an error. Finally if you want some code to execute either way after both, place this in the finally block.

1try
2{
3    functionThatDoesntExists();
4}
5catch (err)
6{
7     alert(err.message);
8}
9finally
10{
11    //Code to execute at the end
12}

Notice the catch section is passed a parameter and I am then alerting a property of this called message. The error parameter can be useful for debugging what actually went wrong and contains a few other parameters.

  • Description
  • Message
  • Name
  • Number
  • Stack

Sometimes you may also want to cause an error to be thrown. You may be asking why, but consider people calling your functions may in-fact pass values that are not valid. You could detect this and throw an error containing some useful information before there incorrect parameter values causes your code to error and a less helpful message given.

1var err = new Error(1, "Oh dear, that's not going to work"); // First parameter is the error number, second is the message
2throw err;

HTML5 Series - Grid

There was a time when an HTML page layout mainly consisted of tables, and lots of them. Tables went inside other tables and complex layouts were achieved through the use of colspans and rowspans. The only problem though was it was a mess.

By using tables the HTML mark-up was dictating the design/layout of the page and if you ever wanted to change anything it was a huge task to undertake. Since then the world has moved on and now most webpages consist mainly of div's. But what if you did want to quite a rigid layout with columns and rows?

HTML5 introduces the Grid style through CSS. Your page can still consist mainly of div's (or anything for that matter), but in your css you set a display property of grid (for now in IE it's -ms-grid). You can then specify a grid-columns and grid-rows property to create a grid within your div.

Child items can be placed in grid cells through grid-row and grid-column properties in the CSS, and if you want something to span more than one cell you can use grid-row-span or grid-column-span.

If you've done any XMAL programming (WPF/Silverlight/Win8/Windows Phone) then this should all sound very similar to XMAL's Grid control.

The example below creates something like this:

1<style>
2        /* Set a grid with 3 columns and 2 rows */
3        div {
4            display: -ms-grid;
5            -ms-grid-columns:200px 200px 200px;
6            -ms-grid-rows:200px 200px;
7        }
8 
9        /* Position the child div's in the grid */
10        div:nth-child(1) {
11            -ms-grid-row: 1;
12            -ms-grid-column: 1;
13        }
14        div:nth-child(2) {
15            -ms-grid-row: 2;
16            -ms-grid-column: 1;
17        }
18        div:nth-child(3) {
19            -ms-grid-row: 1;
20            -ms-grid-column: 2;
21            -ms-grid-row-span:2; /* The middle cell spans 2 rows */
22        }
23        div:nth-child(4) {
24            -ms-grid-row: 1;
25            -ms-grid-column: 3;
26        }
27        div:nth-child(5) {
28            -ms-grid-row: 2;
29            -ms-grid-column: 3;
30        }
31 
32        /* Add a border to the cells */
33        div>div {
34            border: solid 1px black;
35        }
36</style>
37<div class="myGrid">
38    <div></div>
39    <div></div>
40    <div></div>
41    <div></div>
42    <div></div>
43</div>

It's also worth noting that the column/row sizes can be specified using fractions rather than fixed sizes. e.g. The following will produce a grid 600px wide where the middle column is twice the width of the other 2.

1<style>
2        /* Set a grid with 3 columns and 2 rows */
3        div {
4            display: -ms-grid;
5            width:600px;
6            -ms-grid-columns:1fr 2fr 1fr;
7            -ms-grid-rows:200px 200px;
8        }
9</style>

For another great example check out this hands on page from Microsoft Hands on: CSS3 Grid

HTML5 Series - Fonts

It's an all to common story, designer designs a website hands it to a developer who then goes, "what kind of font is that?" and get's the response of some completely unheard of name. The developer then try's to explain what a web safe font is and they agree to use Arial.

With CSS3 custom fonts are now a reality. On the item you are styling you still set the font family in the same way but additionally in your CSS you specify a @font-face rule so the browser can find out what the font is. The @font-face rule should specify a name and the src of the font. e.g.

1@font-face {
2     font-family: myFont;
3     src: url('myFontFileName.ttf');
4}

One point to note different browsers support different font type. Luckily though you can specify multiple sources for your font.

HTML5 Series - Video

Like Audio embedding Video in an HTML5 web page is really simple to do and has a very similar syntax.

The video tag can contain multiple source tags to specify videos in different formats as not all browsers support the same ones, and some text to be displayed if the browser does not support any. The video tag can also have a controls element specified to instruct the browser to display controls for the playback.

1<video controls>
2    <source src="URL of video.mp4" type="video/mp4">
3    <source src="URL of alternate video.ogg" type="video/ogg">
4    Your browser doesn't support viodes
5</video>

You can also set the following tags:

autoplay - Specifies that the video should begin playback immediately

loop - Sets the video to repeat

muted - Mutes the audio on playback

poster - Specifies an image to be shown what the video is downloading

preload - Specifies if an how the video should be loaded when the page loads

It is also possible to control a videos playback through JavaScript. You can reload the element, play and pause that track.

1var v = document.getElementById("myVideo");
2v.play();
3v.pause();
4v.load();