ECMAScript – Trailing Commas

JavaScript allowed trailing commas in array literals since the beginning. Trailing commas in other places have added in the later edition of ECMAScript.

What is trailing comma & why?

Trailing commas is also called as final commas.

It can be used while if you are adding new parameters or property to JavaScript code. If you want to add a new property, you can simply add a new line without modifying the previously last line if that line already uses a trailing comma. This makes version-control diffs cleaner and editing code might be less troublesome.

Arrays, Object literals, function parameters allow trailing commas. However, JSON doesn’t allow trailing commas.

Trailing commas in Array literals

JavaScript allows the trailing commas in arrays.

literals1

If more than one trailing comma is used, an elision (or hole) is produced. An array with holes is called sparse (a dense array has no holes). When iterating arrays for example with Array.prototype.forEach() or Array.prototype.map(), array holes are skipped.

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However, the final comma in the array is ignored.

Object literals

Trailing comma is supported in Object literals from the ECMAScript 5 edition.

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Trailing commas in functions

ECMAScript 2017 allows trailing commas in function parameter lists.

Trailing commas allowed function definition and function calls. Trailing commas don’t affect the length property of function declarations or their arguments object.

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Function parameters with commas only are invalid which will throw SyntaxError.

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What about Internet Explorer Support?

If we are using babel to convert our scripts to native JavaScript to support Internet Explorer. We don’t have to worry about the compatibility.

The babel will convert our scripts with trailing commas to support the IE.

Example: It will remove the commas while building the package.

Left side: Our ECMAScript code

Right side: Equivalent Code generated by babel

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makes version-control diffs cleaner and editing code might be less troublesome

Let’s talk about the main advantage, the Version control support.

Check out the below sample, I’m trying to add an entry to list to two arrays.

One has trailing commas and other not. When we are adding an entry to an array which has trailing comma, the GIT diff looks clean. That’s the main advantage of this whole concept.

When we are having a trailing comma, it only shows the addition of entry.

gitliteral

 

And again, its based every individual to decide whether they want to use this concept or not.

Cheers,

Happy Coding!

Progressive Web Apps – Web App Manifest

The web app manifest is a simple JSON file that gives you, the developer, the ability to control how your app appears to users in areas where they would normally see apps in mobile devices.

Screenshot_20180821-000049

 

Web app manifests are part of a collection of web technologies called progressive web apps, which are websites that can be installed to a device’s homescreen without an app store, along with other capabilities like working offline and receiving push notifications.

And, more importantly, how it behaves when it’s launched from the home screen.

Installs to the homescreen

When a user clicks “Add to homescreen”, they will see the app being added on the homescreen.

At a minimum, the manifest must contain the name of the app and a short_name.

The short_name is used on the home screen and in other places where there is limited space.

It also needs the start_url, the URL the app should open when launched from the home screen.

Defining the manifest metadata

{
"short_name": "Pandiyan",
"name": "Pandiyan Murugan",
"icons": [{
"src": "/img/portrait_small.jpg",
"type": "image/jpg",
"sizes": "192x192"
},
{
"src": "/img/portrait.jpg",
"type": "image/jpg",
"sizes": "512x512"
}
],
"start_url": "/?source=pwa",
"background_color": "#3367D6",
"display": "standalone",
"scope": "/",
"theme_color": "#3367D6"
}

Make sure, the page you specify is cached as part of the app shell. Otherwise, you won’t get the benefits of a cached app shell and your app won’t work offline.

One quick tip.

To track the number of users who are launching your app from their home screen, you can add a query string to the end of your URL.

And use any analytics to track launches, with that query string.

But don’t forget to ensure that you’ve cached the URL with the query string, in your service worker.

Adding icons and Splash screen color

Finally, we need to provide a set of icons for things like the home screen icon and the tab switcher, and splash screen.

The icons parameter takes an array of icons and must include the source, the size of the icon, and the type.

For example, image/jpg.

I recommend providing eight icon sizes,

48 x 48, 96 bx 96, 128 bx 128, 144 x 144,

192 x 192, 256 x 256, 384 x 384 and 512 x 512.

Just make sure you have icons for 1x, 2x, 3x and 4x devices.

Chrome uses the 48 device independent pixel icons for the home screen icon and the tabs footer. And the 128 device pixel icons for the splash screen.

Those are the minimum requirements. But there are a few other helpful things that you should set in the manifest.

The background color, and theme color are used by the browser along with an icon, as part of the splash screen.

Shown the instant the web app is launched, until its first render. As we provide the splash screen color as blue in manifest. The splash screen, icon and short name is displayed while the browser is rendering the application. (http://pandiyan.cool)

Once the app is loaded, the theme color tells the browser, what color to display in the UI elements such as the address bar or the notification tray.

Display and orientation property give you control over how the app is displayed. For example, you can hide the address bar and the back and forward buttons, by setting “display”: “standalone”. Or if you’re building a game that works better in landscape, you can force landscape view by specifying, “orientation”: “landscape”.

Web apps will launch full-screen with no vestiges of a browser. The URL will not be present, nor will traditional browser actions such as bookmarking and navigation controls.

Linking the manifest

When you have created the manifest add a link tag to all the pages that encompass your web app:

<link rel="manifest" href="/manifest.json">

Manifest metadata in browser

To confirm whether the manifest is properly, we can use the chrome DevTools to view the manifest as below

(Switch to Application tab in the Chrome Dev Tools)

manifest

Happy Coding!