What's New in TypeScript 3.5

What's New in TypeScript 3.5

TypeScript 3.5 introduces several optimizations around type-checking and incremental builds.

Less than two weeks after the release candidate, **Microsoft **has shipped the final release of TypeScript 3.5, the increasingly popular programming language that improves upon JavaScript by allowing optional static typing.

The open source, cross-platform language was even said to be "exploding" in popularity in an analyst report earlier this month.

One of the main highlights of this release is actually a fix for a type-checking bug the TypeScript team introduced in v3.4 that caused longer build times and made TypeScript/JavaScript editor operations "unbearably slow."

Other improvements in the compiler/language department as detailed by program manager Daniel Rosenwasser include:

  • The Omit helper type: This lets developers omit certain properties from an object, such as creating a Person type without a location property. See more here.
  • Improved excess property checks in union types: This improves excess property checking in object literals, a feature used to detect typos for when a type isn't expecting a specific property in a union of two constructs. For example, a const created from a union of a Point and Label now will be flagged if it tries to assign a boolean to a property expecting a string. See more here.
  • The --allowUmdGlobalAccess flag: "In TypeScript 3.5, you can now reference UMD global declarations like export as namespace foo; from anywhere -- even modules -- using the new --allowUmdGlobalAccess flag." See more here.
  • Smarter union type checking: This improves upon union type checking that was previously compared each constitutent type in isolation. Now it digs deeper to see if a type is allowable. It stems from a pull request titled "Relate source types covered by a target discriminated union." See more here.
  • Higher order type inference from generic constructors: This stems from a pull request to "support higher order inferences for constructor functions and to permit function type arguments to higher order composition functions to have other members in addition to their single call signature." See more here.

In the editor tooling department, Rosenwasser called out:

  • Smart Select: "TypeScript 3.5 provides an API for editors to expand text selections farther and farther outward in a way that is syntactically aware -- in other words, the editor knows which constructs it should expand out to. This feature is called Smart Select, and the result is that editors don't have to resort to heuristics like brace-matching, and you can expect selection expansion in editors like Visual Studio Code to 'just work"'." See more here.
  • Extract to type alias: Coming from an open source contributor, this is described by Rosenwasser as "a useful new refactoring to extract types to local type aliases." See more here.

Going forward, developers can expect a v3.6 beta on July 12, with the final version set for Aug. 23. It will include expected work items ranging from strongly typed iterators and generators (in the language department) to APIs for --incremental builds and project references (in the compiler department) to a release overhaul (in the infrastructure department) to "Await feedback for more completion priority improvements" (in the editor features department). All of this and much more is detailed in the TypeScript 3.6 iteration plan.

Looking further down the road, the laundry list of new features in the **TypeScript **road map includes:

  • Variadic types
  • Investigate nominal typing support
  • Flattening declarations
  • Implement ES Decorator proposal
  • Implement ES Private Fields
  • Investigate Ambient, Deprecated, and Conditional decorators
  • Investigate partial type argument inference
  • Quick fix to Scaffold local @types packages
  • Investigate error messages in haiku or iambic pentameter
  • Decorators for function expressions/arrow functions

Note that the possibility of providing error messages in haiku or iambic parameter is still a hot item, with our own .NET expert columnist Peter Vogel offering up the following nugget in a comment on an earlier article that mentioned the poetic PR:

Reference is null.> * Reflect: Cold nature also*> * Abhors a vacuum.*
However, Rosenwasser has said the issue has taken a back seat to more important issues, even throwing some shade on the original idea: "Besides, we'd probably do limericks first anyway. A haiku doesn't even rhyme."

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React Web Development: A Guide to Develop Progressive Web Applications

React Web Development: A Guide to Develop Progressive Web Applications

Outperform your competition with progressive web development and React.

Progressive web applications (PWAs) quickly gained popularity because they are web performance applications based on fast performance, streamlined to provide a mobile app-like experience. PWAs are built using HTML, CSS, and JavaScript to create a level of availability and performance equivalent to that of native mobile applications. They respond quickly, consume less data, store more space, and support push notifications and offline use in the browser.

Building a progressive web application has now become the web development trend that every business wants to follow. Significant players like Twitter and Flipboard have recently rolled out their progressive web apps to provide a mobile experience for users, without requiring them to install the app. In this article, you will learn how to build a progressive web application using React. Let's get started.

Step One — Set up the React Application

First, create a React application with create-react-app. To do so, you need to run the following commands:

  • npm install -g create-react-app
  • create-react-app pwa-app

Now, install React Router:

You need to replace the content of src / App.js using the code below to get a basic template with navigation.

import React, { Component } from 'react';
import { Router, browserHistory, Route, Link } from 'react-router';
import './App.css';

const NavBar = () => (
<div className="navbar">
<Link to="/">Feed</Link>
<Link to="/profile">Profile</Link>
</div>
);

const Template = ({ title }) => (
<div>
<NavBar />
<p className="page-info">
This is the {title} page.
</p>
</div>
);

const Feed = (props) => (
<Template title="Feed"/>
);

const Profile = (props) => (
<Template title="Profile"/>
);

class App extends Component {
render() {
return (
<Router history={browserHistory}>
<Route path="/" component={Feed}/>
<Route path="/profile" component={Profile}/>
</Router>
);
}
}
export default App;

Now, you'll have to update the default styles by replacing your src/App.css with the styles below to make your application look clean.

.navbar {
background-color: #01C8E5;
text-align: center;
}

.navbar a {
display: inline-block;
padding: 10px;
color: #fff;
text-decoration: none;
}

.page-info {
text-align: center;
font-weight: bold;
}

Then, run npm start to test the application in the browser. It is basically an application with two routes. Now, you will convert it to PWA.

Step Two — Lighthouse Setting and Auditing

Lighthouse is an automated open-source tool for testing applications against PWA checklists. It facilitates audits for accessibility, performance, and more.

Check your application with Lighthouse. Click the Lighthouse icon from the top right corner in Chrome and then click the "Create Report" button. The generated report will look like this:

Creating a report to test your PWA with Lighthouse

Fix all failed audits.

Step 3 — Sign Up for a Service Staff

Service employees are proxy servers that connect the application and the network. With Service Worker, you will have to block network requests and save cached files. It allows your application to work even with an unavailable system.

Create an empty worker.js file in your application's general directory and add the following code to that file.

// Flag for enabling cache in production
var doCache = false;

var CACHE_NAME = 'pwa-app-cache';

// Delete old caches
self.addEventListener('activate', event => {
const currentCachelist = [CACHE_NAME];
event.waitUntil(
caches.keys()
.then(keyList =>
Promise.all(keyList.map(key => {
if (!currentCachelist.includes(key)) {
return caches.delete(key);
}
}))
)
);
});

// This triggers when user starts the app
self.addEventListener('install', function(event) {
if (doCache) {
event.waitUntil(
caches.open(CACHE_NAME)
.then(function(cache) {
fetch('asset-manifest.json')
.then(response => {
response.json();
})
.then(assets => {
// We will cache initial page and the main.js
// We could also cache assets like CSS and images
const urlsToCache = [
'/',
assets['main.js']
];
cache.addAll(urlsToCache);
})
})
);
}
});

// Here we intercept request and serve up the matching files
self.addEventListener('fetch', function(event) {
if (doCache) {
event.respondWith(
caches.match(event.request).then(function(response) {
return response || fetch(event.request);
})
);
}
});

Now, check if the browsers support service staff and then register worker.js. To do this, you need to add the following script to the file public/index.html (note that shrink-to-fit=no in the viewport meta tag has been deleted).

<!doctype html>
<html lang="en">
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<meta name="theme-color" content="#000000">
<link rel="manifest" href="%PUBLIC_URL%/manifest.json">
<link rel="shortcut icon" href="%PUBLIC_URL%/favicon.ico">
<title>React App</title>
</head>
<body>
<noscript>
You need to enable JavaScript to run this app.
</noscript>
<div id="root"></div>
<script>
if ('serviceWorker' in navigator) {
window.addEventListener('load', function() {
navigator.serviceWorker.register('worker.js').then(function(registration) {
console.log('Worker registration successful', registration.scope);
}, function(err) {
console.log('Worker registration failed', err);
}).catch(function(err) {
console.log(err);
});
});
} else {
console.log('Service Worker is not supported by browser.');
}
</script>
</body>
</html>

You must restart your application and reload the browser after which you will see the Successful registration of member workers on the developer console. Now, recreate the Lighthouse report.

Step 4 - Improve the Progressive Nature of the Application

Your application will display an original blank div until the JavaScript loads and React hooks the original route. You must make sure your application works without downloading JS and displaying a bit of CSS and HTML before React takes effect. Your updated Index.html will look like this:

<!doctype html>
<html lang="en">
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<meta name="theme-color" content="#000000">
<link rel="manifest" href="%PUBLIC_URL%/manifest.json">
<link rel="shortcut icon" href="%PUBLIC_URL%/favicon.ico">
<title>React App</title>
<style type="text/css">
body {
margin: 0;
padding: 0;
font-family: sans-serif;
}
.navbar {
background-color: #01C8E5;
text-align: center;
}
.navbar a {
display: inline-block;
padding: 10px;
color: #fff;
text-decoration: none;
}
.page-info {
text-align: center;
font-weight: bold;
}
</style>
</head>
<body>
<noscript>
You need to enable JavaScript to run this app.
</noscript>
<div id="root">
<div class="navbar">
<a href="/">Feed</a>
</div>
<p class="page-info">
Loading an awesome app...
</p>
</div>
<script>
if ('serviceWorker' in navigator) {
window.addEventListener('load', function() {
navigator.serviceWorker.register('worker.js').then(function(registration) {
console.log('Worker registration successful', registration.scope);
}, function(err) {
console.log('Worker registration failed', err);
}).catch(function(err) {
console.log(err);
});
});
} else {
console.log('Service Worker is not supported by browser.');
}
</script>
</body>
</html>

Now, use Lighthouse to retest your application, and you'll see an improvement in the performance of the application.

Step 5 - Add the Splash Icon

You are required to add a 512x512 icon to display on the screen. To do so, you will have to update the manifest.json file and add the t0 icon to the public directory.

{
"short_name": "React App",
"name": "Create React App Sample",
"icons": [
{
"src": "icon-192x192.png",
"sizes": "192x192",
"type": "image/png"
},
{
"src": "icon-512x512.png",
"sizes": "512x512",
"type": "image/png"
}
],
"start_url": "/",
"display": "standalone",
"theme_color": "#000000",
"background_color": "#ffffff"
}

Also, use the following meta tags to allow the browser to determine that your application is a PWA.

<!-- Tell the browser it's a PWA -->
<meta name="mobile-web-app-capable" content="yes">
<!-- Tell iOS it's a PWA -->
<meta name="apple-mobile-web-app-capable" content="yes">
Step 6 — Implement PWA

Now, only HTTPS is missing, and the cache can be fixed after you deploy the application. Update the doCache flag with true in the worker.js file. Create a new project in the firebase dashboard and name it "Pwa Application." Then, run the following command in the project directory:

npm install -g firebase-tools
firebase login
firebase init

Your Firebase.json will look like this:

{
"hosting": {
"public": "build",
"rewrites": [
{
"source": "**",
"destination": "/index.html"
}
]
}
}

After initializing, building and deploying your application.

  • npm run build
  • firebase deploy

You will see results after you test the application using Lighthouse on the deployed URL.

Final product with Lighthouse

Finally, you have created your first progressive web application with React.js!

Originally published by Manoj Kumar Bardhan at  dzone.com

=======================================================

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