Meaning: You can use the variable before it is declared:Meaning: The block of code is aware of the var is scoped to the nearest function block and let is scoped to the nearest enclosing block, which can be smaller than a function block. Recently I attended a 15 minute lightning talk just on this topic, with many great details on JavaScript parsing, execution context, and hoisting.But, I found that I was still having trouble explaining the concept myself until I wrote it down this way:This is how many programmers expect variables to work, because most programming languages only have block scope.Here, immutable means the reference cannot be changed, since primitive values like numbers and strings are also immutable in JavaScript.Note that objects are an exception, because their properties can still be changed. [W]hen Javascript compiles all of your code, all variable declarations using Note that the variable declaration is hoisted, but the value assignation is not. var vs let vs const in JavaScript January 01, 2019. The var variables.

Scope of a variable, in simple terms is the section of code where the variable is visible.

It is a new feature introduced in Here , calCube is regular function and AcalCube is arrow function.Arvind Pande holds a Master of Engineering degree and obtained dual Microsoft Certifications(MCTS).

outside the block:Redeclaring a variable inside a block will not redeclare the variable outside

Tutorials, references, and examples are constantly reviewed to avoid errors, but we cannot warrant full correctness of all content. var and let are both used for variable declaration in javascript but the difference between them is that var is function scoped and let is block scoped. JavaScript is a dynamic type language, means we don’t need to specify type of the variable because it is dynamically used by JavaScript engine. But before we actually dive into the differences between var, let, and const, there are some prerequisites you need to know first. So if you try to use a let variable before declaration, you'll get a Reference Error.

That means hoisting can produce results that you might not expect:When a function returns a function, that is when the concept of closures becomes more relevant.

JavaScript variables are case sensitive. so once we linked JavaScript file with web page, we can call any function for multiple times.A JavaScript variable is a name of storage location. Depending on personal preference, some programmers treat const objects as actually immutable and try not to change their data at all.
In this article, we have understood how variables are declared in JavaScript, and the differences between the variable types - var, let and const. Outside its scope, the variable does not exist. These variable types are unique in their own way and serve to make code development efficient, however, it is advised to use let whenever possible and const whenever the value of the variable is to remain constant. variable name must start with a letter (a to z or A to Z), underscore( _ ), or dollar( $ ) sign.here, let a1=100 ,b=20 is variable declaration. here you can code download the difference let and var variable declarations, regular and arrow function definitions with examples.we can directly write JavaScript commands inside script tags in HTML code.Write above code in notepad editor, save file as test1.html and open file in any browser application from your machine.here write method of document object, Writes specified text directly to the HTML document. If you'd like to contribute to the data, please check out variable name must start with a letter (a to z or A to Z), underscore( _ ), or dollar( $ ) sign.There are two types of variables in JavaScript : local variable and global variable. Both var and let are used to define variables.

It is accessible within the function or block only.A JavaScript global variable is accessible from any function. There are two ways you can declare variables in JavaScript let and var. In this way, let works very much like var.

All the scripts in page can access and modify global variable.Arrow functions allow us to write shorter function syntax.