Julie  Donnelly

Julie Donnelly

1602380460

Closures and Lexical Scoping in JavaScript

Variables in JavaScript have two types of scoping i.e. Local and Global scope. If any variable is declared inside a function, then it is a local variable and if the variable is declared outside the function then it is global variable. The scope of variables is defined by their position in the code.

Lexical Scope

JavaScript follows Lexical scoping for functions. Lexical scope means any child’s scope has access to the variables defined in parent’s scope i.e. inner functions can access the global variables.

var a = 5;

function sum() {
  return a + 6;
}
console.log(sum()); // 11

In the above example, function sum() is using global variable "a" to perform the addition. That means variable "a" is in scope of sum().

#closure #lexical-scope #javascript #javascript-tips #web-development

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Buddha Community

Closures and Lexical Scoping in JavaScript
Julie  Donnelly

Julie Donnelly

1602380460

Closures and Lexical Scoping in JavaScript

Variables in JavaScript have two types of scoping i.e. Local and Global scope. If any variable is declared inside a function, then it is a local variable and if the variable is declared outside the function then it is global variable. The scope of variables is defined by their position in the code.

Lexical Scope

JavaScript follows Lexical scoping for functions. Lexical scope means any child’s scope has access to the variables defined in parent’s scope i.e. inner functions can access the global variables.

var a = 5;

function sum() {
  return a + 6;
}
console.log(sum()); // 11

In the above example, function sum() is using global variable "a" to perform the addition. That means variable "a" is in scope of sum().

#closure #lexical-scope #javascript #javascript-tips #web-development

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

Brad  Hintz

Brad Hintz

1598702760

A practical example of Javascript closures

ost developers today, know about closures in Javascript. Don’t be sad if you don’t, it’s not something you generally use on your every-day work (well, you may, but it’s not so common).

losures are something that many companies would like you to know before working for them, therefore, chances are they’ll ask you something related with this topic, or even more, they could make you write a practical example of it.

On this story, I’m gonna tell you about a small function I was asked to develop on an interview a while ago, that involved the use of closures for its solution.

Let’s start with the premise:

Can you write a function that will solve the following test case?

let result = sum(1)(2)(3)();

console.log(result === 6 ? 'SUCCESS' : 'ERROR');

The function we need to create will sum the values sent as a parameter and will accumulate them. Also, it will return another function for the next value to be passed on. If we don’t send any value to it, it will return the accumulated value.

It looks fairly simple at first, but let’s take a look into it:

const sum = (value) => {
  let accum = 0;

  if (value) {
    accum += value;
    const innerSum = (value) => { /*TODO*/ };
  } else {
    return accum;
  }
};
console.log(sum());
0

That’s a good start. First, we create the function called sum that will take a value as a parameter. If that value exists, we will sum the value to the accum and return a function to keep adding values (TODO).

#currying #javascript-interview #javascript #closures-functions #closure

Houston  Sipes

Houston Sipes

1595523600

Quick Wins With Code: Closures in JavaScript

Seeing as MDN’s page on closures defines it extremely well, I’m not going to reinvent the wheel here:

A closure is the combination of a function bundled together (enclosed) with references to its surrounding state (the lexical environment).

Let’s unpack this concept a bit.

The first thing I want to point out is that whenever you define a function, you are making a choice about its lexical environment, whether intentional or unintentional, conscious or…maybe you’re unconscious. I don’t know.

In many cases, the lexical environment of a function is just the global scope, because that is where you created it. Don’t worry, there’s nothing wrong with that.

**But the value of a closure becomes more obvious when you intentionally enclose a function into its own lexical environment. **One of the ways you can do this is by wrapping it inside another function. You’ve now created a more specific, local scope.

Here’s an example:

	function rocket(name, fc) {
	  let _name = name;
	  let _fuelConsumption = fc;
	  let _gas = 100;
	  let _miles = 0;

	  function fly() {
	    while (_gas > 0) {
	      _miles++;
	      _gas -= _fuelConsumption
	    };
	    console.log(`${_name} flew ${_miles} mile${_miles === 1 ? '' : 's'}.`);
	  };

	  return { fly };
	};

	let teslaRocket = rocket('Tesla Rocket', 1);
	let sputnik = rocket('Sputnik', 1.5);

	teslaRocket.fly();
	// Tesla Rocket flew 100 miles.
	sputnik.fly();
	// Sputnik flew 67 miles.

Here we have a rocket function, which has some local variables, and an inner fly function. When I call rocket, it returns a unique instance of an object with the fly function stored inside that object (line 15). It’s important to note that I’m not actually calling fly yet. I’m just returning an object that has the fly function inside it.

Each time I call the rocket function, I’m returning a separate instance of the fly function, and that instance of fly is actually holding on to its own instance of its lexical environment, even after rocket has completed running.

That right there is the power of a closure: Each time I call rocket, I’m creating an instance of fly that has a persisting reference to a unique lexical environment.

You can see how this specific use case could be valuable if you’re trying to do something object oriented. We’ve encapsulated state and behavior in a persisting, reusable manner! And we didn’t use classconstructorthis, or new. How about that.

One other nice thing about doing object oriented programming in this manner is that your state is actually private and inaccessible compared to when you use class syntax from ES2015. You can’t access the name of a rocket with sputnik._name (unless you added it to the returned object of rocket on line 15, but you shouldn’t do that).

The power to keep private state truly inaccessible is a really good thing. It tells readers how the function should and should not be used. Keep private variables private. This also gives you the option to implement a true “read only” paradigm, if you wanted to.

For example:

	function rocket(name, fc) {
	  let _name = name;
	  let _fuelConsumption = fc;
	  let _gas = 100;
	  let _miles = 0;

	  function fly() {
	    while (_gas > 0) {
	      _miles++;
	      _gas -= _fuelConsumption
	    };
	    console.log(`${_name} flew ${_miles} mile${_miles === 1 ? '' : 's'}.`);
	  };

	  return { 
	    fly,
	    get name() {
	      return _name;
	    }
	  };
	};

	let teslaRocket = rocket('Tesla Rocket', 1);
	let sputnik = rocket('Sputnik', 1.5);

	teslaRocket.fly();
	// Tesla Rocket flew 100 miles.
	console.log(teslaRocket.name);
	// Tesla Rocket
	sputnik.fly();
	// Sputnik flew 67 miles.
	console.log(sputnik.name);
	// Sputnik

I’ve added name access in the object returned by rocket on lines 17–19, using get syntax. I can now read the _name property, but I don’t have the ability to change it. That’s exactly the kind of guardrail that I wanted to implement. Great success!

#closure #web-dev-bootcamps #code-camp #javascript #lexical-scope #visual studio code

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