Nina Diana

Nina Diana

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Javascript's new features in 2020

ECMAScript 2015, also known as ES6, was a major release that took six years to finalize. Since then, Technical Committee 39 (TC39), the body in charge of developing the ECMAScript standard, has been releasing a new edition of the standard every year. This annual release cycle has streamlined the process and made new features rapidly available, which the JavaScript community has welcomed.

This year, ECMAScript 2020 (or ES2020 for short) will be released. The new features include Object.fromEntries(), trimStart(), trimEnd(), flat(), flatMap(), description property for symbol objects, optional catch binding, and more.

The good news is that these features have already been implemented in the latest versions of Firefox and Chrome, and they can also be transpiled so that older browsers are able to process them. In this post, we will take a good look at these features and see how they upgrade the language.

1. Object.fromEntries()

Transforming data from one format to another is very common in JavaScript. To facilitate the conversion of objects into arrays, ES2017 introduced the Object.entries() method. This method takes an object as an argument and returns an array of the object’s own enumerable string-keyed property pairs in the form of [key, value]. For example:

const obj = {one: 1, two: 2, three: 3};

console.log(Object.entries(obj));    
// => [["one", 1], ["two", 2], ["three", 3]]

But what if we wanted to do the opposite and convert a list of key-value pairs into an object? Some programming languages, such as Python, provide the dict() function for this purpose. There’s also the _.fromPairs function in Underscore.js and Lodash.

ES2019 aims to bring a similar feature to JavaScript by introducing the Object.fromEntries() method. This static method allows you to easily transform a list of key-value pairs into an object:

const myArray = [['one', 1], ['two', 2], ['three', 3]];
const obj = Object.fromEntries(myArray);

console.log(obj);    // => {one: 1, two: 2, three: 3}

As you can see, Object.fromEntries() is simply the reverse of Object.entries(). While it was previously possible to achieve the same result, it wasn’t very straightforward:

const myArray = [['one', 1], ['two', 2], ['three', 3]];
const obj = Array.from(myArray).reduce((acc, [key, val]) => Object.assign(acc, {[key]: val}), {});

console.log(obj);    // => {one: 1, two: 2, three: 3}

Keep in mind that the argument passed to Object.fromEntries()can be any object that implements the iterable protocol as long as it returns a two-element, array-like object.

For example, in the following code, Object.fromEntries() takes a Map object as an argument and creates a new object whose keys and corresponding values are given by the pairs in the Map:

const map = new Map();
map.set('one', 1);
map.set('two', 2);

const obj = Object.fromEntries(map);

console.log(obj);    // => {one: 1, two: 2}

The Object.fromEntries() method is also very useful for transforming objects. Consider the following code:

const obj = {a: 4, b: 9, c: 16};

// convert the object into an array
const arr = Object.entries(obj);

// get the square root of the numbers
const map = arr.map(([key, val]) => [key, Math.sqrt(val)]);

// convert the array back to an object
const obj2 = Object.fromEntries(map);

console.log(obj2);  // => {a: 2, b: 3, c: 4}

This code converts values in an object into their square root. To do that, it first converts the object into an array, then uses the map() method to get the square root of values in the array. The result is an array of arrays that can be converted back to an object.

Another situation in which Object.fromEntries() comes in handy is when working with the query string of a URL, as shown in this example:

const paramsString = 'param1=foo&param2=baz';
const searchParams = new URLSearchParams(paramsString);

Object.fromEntries(searchParams);    // => {param1: "foo", param2: "baz"}

In this code, a query string is passed to the URLSearchParams() constructor. Then the return value, which is a URLSearchParams object instance, is passed to the Object.fromEntries() method. The result is an object containing each parameter as a property.

The Object.fromEntries() method is currently a stage 4 proposal, which means it’s ready for inclusion in the ES2019 standard.

2. trimStart() and trimEnd()

The trimStart() and trimEnd() methods are technically the same as trimLeft() and trimRight(). These methods are currently stage 4 proposals and will be added to the specification for consistency with padStart() and padEnd(). Let’s look at some examples:

const str = "   string   ";

// es2019
console.log(str.trimStart());    // => "string   "
console.log(str.trimEnd());      // => "   string"

// the same as
console.log(str.trimLeft());     // => "string   "
console.log(str.trimRight());    // => "   string"

For web compatibility, trimLeft() and trimRight() will remain as aliases for trimStart() and trimEnd().

3. flat() and flatMap()

The flat() method enables you to easily concatenate all sub-array elements of an array. Consider the following example:

const arr = ['a', 'b', ['c', 'd']];
const flattened = arr.flat();

console.log(flattened);    // => ["a", "b", "c", "d"]

Previously, you’d have to use reduce() or concat() to get a flat array:

const arr = ['a', 'b', ['c', 'd']];
const flattened = [].concat.apply([], arr);

// or
// const flattened =  [].concat(...arr);

console.log(flattened);    // => ["a", "b", "c", "d"]

Note that if there are any empty slots in the provided array, they will be discarded:

const arr = ['a', , , 'b', ['c', 'd']];
const flattened = arr.flat();

console.log(flattened);    // => ["a", "b", "c", "d"]

flat() also accepts an optional argument that specifies the number of levels a nested array should be flattened. If no argument is provided, the default value of 1 will be used:

const arr = [10, [20, [30]]];

console.log(arr.flat());     // => [10, 20, [30]]
console.log(arr.flat(1));    // => [10, 20, [30]]
console.log(arr.flat(2));    // => [10, 20, 30]

The flatMap() method combines map() and flat() into one method. It first creates a new array with the return value of a provided function and then concatenates all sub-array elements of the array. An example should make this clearer:

const arr = [4.25, 19.99, 25.5];

console.log(arr.map(value => [Math.round(value)]));    
// => [[4], [20], [26]]

console.log(arr.flatMap(value => [Math.round(value)]));    
// => [4, 20, 26]

The depth level that the array will be flattened is 1. If you want to remove an item from the result, simply return an empty array:

const arr = [[7.1], [8.1], [9.1], [10.1], [11.1]];

// do not include items bigger than 9
arr.flatMap(value => {
  if (value >= 10) {
    return [];
  } else {
    return Math.round(value);
  }
});  

// returns:
// => [7, 8, 9]

In addition to the current element being processed, the callback function will also receive the index of the element and a reference to the array itself. The flat() and flatMap() methods are currently stage 4 proposals.

4. Description property for Symbol objects

When creating a Symbol, you can add a description to it for debugging purposes. Sometimes, it’s useful to be able to directly access the description in your code.

This ES2019 proposal adds a read-only description property to the Symbol object, which returns a string containing the description of the Symbol. Here are some examples:

let sym = Symbol('foo');
console.log(sym.description);    // => foo

sym = Symbol();
console.log(sym.description);    // => undefined

// create a global symbol
sym = Symbol.for('bar');
console.log(sym.description);    // => bar

5. Optional catch binding

The catch binding in a try … catch statement would not always be used. Consider the following code:

try {
  // use a feature that the browser might not have implemented
} catch (unused) {
  // fall back to an already implemented feature 
}

There is no use for the catch binding in this code. However, it still should be used to avoid a SyntaxError. This proposal makes a small change to the ECMAScript specification that allows you to omit the catch binding and its surrounding parentheses:

try {
  // use a feature that the browser might not have implemented
} catch {
  // do something that doesn’t care about the value thrown
}

Bonus: ES2020 String.prototype.matchAll

The matchAll() method is a stage 4 ES2020 proposal that returns an iterator object for all matches — including capturing groups — against a regular expression.

For consistency with the match() method, TC39 selected “matchAll” over other suggested names such as “matches” or Ruby’s “scan.” Let’s look at a simple example:

const re = /(Dr\. )\w+/g;
const str = 'Dr. Smith and Dr. Anderson';
const matches = str.matchAll(re);

for (const match of matches) {
  console.log(match);
}

// logs:
// => ["Dr. Smith", "Dr. ", index: 0, input: "Dr. Smith and Dr. Anderson", groups: undefined]
// => ["Dr. Anderson", "Dr. ", index: 14, input: "Dr. Smith and Dr. Anderson", groups: undefined]

The capturing group in this regular expression matches the characters “Dr” followed by a dot and a space. \w+ matches any word character one and more times. And the g flag instructs the engine to search for the pattern throughout the string.

Previously, you’d have to use the exec() method in a loop to achieve the same result, which wasn’t very efficient:

const re = /(Dr\.) \w+/g;
const str = 'Dr. Smith and Dr. Anderson';
let matches;

while ((matches = re.exec(str)) !== null) {
  console.log(matches);
}

// logs:
// => ["Dr. Smith", "Dr.", index: 0, input: "Dr. Smith and Dr. Anderson", groups: undefined]
// => ["Dr. Anderson", "Dr.", index: 14, input: "Dr. Smith and Dr. Anderson", groups: undefined]

It’s important to note that although the match() method can be used with the global flag g to access all matches, it doesn’t provide capturing groups or index position of the matches. Compare:

const re = /page (\d+)/g;
const str = 'page 2 and page 10';

console.log(str.match(re));    
// => ["page 2", "page 10"]

console.log(...str.matchAll(re)); 
// => ["page 2", "2", index: 0, input: "page 2 and page 10", groups: undefined] 
// => ["page 10", "10", index: 11, input: "page 2 and page 10", groups: undefined]

Wrapping up

In this post, we have taken a close look at several key features introduced in ES2020, including Object.fromEntries(), trimStart(), trimEnd(), flat(), flatMap(), description property for symbol objects, and optional catch binding.

Despite the fact that these features are not fully implemented by some browser vendors yet, you can still use them in your projects thanks to Babel and other JavaScript transpilers.

ECMAScript’s pace of development has stepped up in recent years, and new features are being introduced and implemented every so often, so be sure to check out the list of finished proposals to get updated on what’s new. Do you have some tips? Share them in the comments!

#javascript #ES2019 #es6 #es5

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Brain  Crist

Brain Crist

1594753020

Citrix Bugs Allow Unauthenticated Code Injection, Data Theft

Multiple vulnerabilities in the Citrix Application Delivery Controller (ADC) and Gateway would allow code injection, information disclosure and denial of service, the networking vendor announced Tuesday. Four of the bugs are exploitable by an unauthenticated, remote attacker.

The Citrix products (formerly known as NetScaler ADC and Gateway) are used for application-aware traffic management and secure remote access, respectively, and are installed in at least 80,000 companies in 158 countries, according to a December assessment from Positive Technologies.

Other flaws announced Tuesday also affect Citrix SD-WAN WANOP appliances, models 4000-WO, 4100-WO, 5000-WO and 5100-WO.

Attacks on the management interface of the products could result in system compromise by an unauthenticated user on the management network; or system compromise through cross-site scripting (XSS). Attackers could also create a download link for the device which, if downloaded and then executed by an unauthenticated user on the management network, could result in the compromise of a local computer.

“Customers who have configured their systems in accordance with Citrix recommendations [i.e., to have this interface separated from the network and protected by a firewall] have significantly reduced their risk from attacks to the management interface,” according to the vendor.

Threat actors could also mount attacks on Virtual IPs (VIPs). VIPs, among other things, are used to provide users with a unique IP address for communicating with network resources for applications that do not allow multiple connections or users from the same IP address.

The VIP attacks include denial of service against either the Gateway or Authentication virtual servers by an unauthenticated user; or remote port scanning of the internal network by an authenticated Citrix Gateway user.

“Attackers can only discern whether a TLS connection is possible with the port and cannot communicate further with the end devices,” according to the critical Citrix advisory. “Customers who have not enabled either the Gateway or Authentication virtual servers are not at risk from attacks that are applicable to those servers. Other virtual servers e.g. load balancing and content switching virtual servers are not affected by these issues.”

A final vulnerability has been found in Citrix Gateway Plug-in for Linux that would allow a local logged-on user of a Linux system with that plug-in installed to elevate their privileges to an administrator account on that computer, the company said.

#vulnerabilities #adc #citrix #code injection #critical advisory #cve-2020-8187 #cve-2020-8190 #cve-2020-8191 #cve-2020-8193 #cve-2020-8194 #cve-2020-8195 #cve-2020-8196 #cve-2020-8197 #cve-2020-8198 #cve-2020-8199 #denial of service #gateway #information disclosure #patches #security advisory #security bugs

Rahul Jangid

1622207074

What is JavaScript - Stackfindover - Blog

Who invented JavaScript, how it works, as we have given information about Programming language in our previous article ( What is PHP ), but today we will talk about what is JavaScript, why JavaScript is used The Answers to all such questions and much other information about JavaScript, you are going to get here today. Hope this information will work for you.

Who invented JavaScript?

JavaScript language was invented by Brendan Eich in 1995. JavaScript is inspired by Java Programming Language. The first name of JavaScript was Mocha which was named by Marc Andreessen, Marc Andreessen is the founder of Netscape and in the same year Mocha was renamed LiveScript, and later in December 1995, it was renamed JavaScript which is still in trend.

What is JavaScript?

JavaScript is a client-side scripting language used with HTML (Hypertext Markup Language). JavaScript is an Interpreted / Oriented language called JS in programming language JavaScript code can be run on any normal web browser. To run the code of JavaScript, we have to enable JavaScript of Web Browser. But some web browsers already have JavaScript enabled.

Today almost all websites are using it as web technology, mind is that there is maximum scope in JavaScript in the coming time, so if you want to become a programmer, then you can be very beneficial to learn JavaScript.

JavaScript Hello World Program

In JavaScript, ‘document.write‘ is used to represent a string on a browser.

<script type="text/javascript">
	document.write("Hello World!");
</script>

How to comment JavaScript code?

  • For single line comment in JavaScript we have to use // (double slashes)
  • For multiple line comments we have to use / * – – * /
<script type="text/javascript">

//single line comment

/* document.write("Hello"); */

</script>

Advantages and Disadvantages of JavaScript

#javascript #javascript code #javascript hello world #what is javascript #who invented javascript

Hire Dedicated JavaScript Developers -Hire JavaScript Developers

It is said that a digital resource a business has must be interactive in nature, so the website or the business app should be interactive. How do you make the app interactive? With the use of JavaScript.

Does your business need an interactive website or app?

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The technology used to develop the overall app by the developers from WebClues Infotech is at par with the latest available technology.

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#hire dedicated javascript developers #hire javascript developers #top javascript developers for hire #hire javascript developer #hire a freelancer for javascript developer #hire the best javascript developers

Niraj Kafle

1589255577

The essential JavaScript concepts that you should understand

As a JavaScript developer of any level, you need to understand its foundational concepts and some of the new ideas that help us developing code. In this article, we are going to review 16 basic concepts. So without further ado, let’s get to it.

#javascript-interview #javascript-development #javascript-fundamental #javascript #javascript-tips

Ajay Kapoor

1626321063

JS Development Company India | JavaScript Development Services

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