JavaScript Const

Const is a keyword that indicates a constant. It describes an entity that cannot be changed at runtime. We cannot reassign a constant. With constants we lose the ability to modify variables at runtime and we gain run-time validation.

One of the most important things is that you should try to keep things simple!


When Should You Use

When Should You Use var, const Or let?

It is important to understand Global-Scope, Function-Scope and Block-Scope to know when you may use the different statements.

Global Scope

Variables declared Globally (outside any block or function) have Global Scope.

Be careful with using Global Scope.

var car = "Byton";
 
// code CAN use variable car
 
function carFunction() {
     // code CAN also use variable car 
}

Function Scope

Variables declared inside a function have Function Scope.

// code can NOT use variable car
 
function carFunction() {
     var car = "Byton";
     // code CAN use variable car
}
 
// code can NOT use variable car

Block Scope

Variables declared inside a block {} have Block Scope.

{ 
     var car = "Byton"; 
}
// code CAN use variable car

Learn more about JavaScript Scope Learn more about JavaScript Hoisting

JavaScript Const

ECMAScript 2015 introduced two important JavaScript keywords: let and const.

Constants are Block-Scoped, much like variables defined using the let statement.

To keep things simple - Use const to identify a constant. Use let to define a variable.

The scope of a constant can be either global or local to the block where it is declared.

Take a look at the example to understand this.

JS JavaScript - JavaScript Const

var car = "Tesla";
const fuel = "Electric";
// Here car have the value "Tesla"
{ 
    const car = "Chrysler";
    // Here car have the value "Chrysler"
 
    var fuel = "petrol";   // This will give a syntax error
}
// Here the variable car have the value "Tesla"
 

Learn more about JavaScript Var Learn more about JavaScript Let

Const Assigned When Declared

Const variables must assign a value when they are declared

JS JavaScript - Const Assigned When Declared

// This is not allowed
const car;
car = "Mercedes";
 
// This is correct syntax
const car = "Mercedes";

Const continue

The keyword const need some more explanation.

Const defines a constant reference - it is a bit confusing.

It is not possible to change constant primitive values, but we can change the values of constant objects

Take a look at the example to understand this.

Primitive Values

A primitive const value cannot be changed

const car = "Byton";

// This will give an error
car = "Mercedes";

// This will give an error
car = car + " and Mercedes";

Objects

It is possible to change the properties of a constant object

// Create a const object
const car = {type:"Byton", model:"kbyte", color:"red"};
 
// It is possible to change a property
car.color = "blue";
 
// It is possible to add a property
car.engine = "Electric";

It is NOT possible to reassign a constant object

const car = {type:"Byton", model:"kbyte", color:"red"};
 
// This gives a syntax error
car = {type:"Tesla", model:"Model X", color:"red"};

Arrays

It is possible to change elements in a constant array

// A constant array
const cars = ["Byton", "Tesla", "Audi"];
 
// It is possible to change an element
cars[2] = "Mercedes";
 
// It is possible to add an element
cars.push("BMW");

It is NOT possible to reassign a constant array

// A constant array
const cars = ["Byton", "Tesla", "Audi"];
 
// This gives a syntax error
cars = ["BMW", "Polestar", "Lexus"];

Learn more about JavaScript Variables Learn more about JavaScript Comments
BACK TO TOP






Check this out

JS JavaScript: break

The break statement terminates a current loop or a switch statement.

The continue statement "jumps over" one iteration in the current loop.

JS JavaScript: Numbers Methods

Number methods can help you when working with number datatypes. The number methods are improved in ES6 (ECMAScript 6).

Keep reading to understand how the number methods and properties may help you.

JS JavaScript: Random

JavaScript have a Random number function. The method can generate a number in a specific range. The number can not be reasonably be predicted.

JS JavaScript: Events

Events are actions or occurrences that happen to HTML elements.

JavaScript can act when an HTML Event occurs.

Events can represent everything from basic user interactions to automated notifications of things happening in the rendering model.


BACK TO TOP

JavaScript is one of the 3 core language technologies of the World Wide Web that all web developers must learn:

1.      HTML to define the content of web pages.

2.      CSS to specify the layout of web pages.

3.      JavaScript to program the behavior of web pages.

JavaScript is a scripting or programming language that allows you to implement complex things on web pages. Every time a web page does more than just sit there and display static information for you to look at, displaying timely content updates, interactive maps, animated 2D/3D graphics, scrolling video jukeboxes, etc. − you can bet that JavaScript is probably involved.


The benefits of using JavaScript are:

1.      You can validate user input before sending the page off to the server. This saves server traffic, which means less load on your server.

2.      Immediate feedback to the visitors − They don't have to wait for a page reload to see if they have forgotten to enter something.

3.      Increased interactivity − You can create interfaces that react when the user hovers over them with a mouse or activates them via the keyboard.

4.      Richer interfaces − You can use JavaScript to include such items as drag-and-drop components and sliders to give a Rich Interface to your site visitors.


BACK TO TOP

Need more Honney

NDC Conferences

The NDC Conferences (Norwegian Developers Conference) are one of the world`s largest independent software conferences for .NET & Agile development. The conference covers everything you need to know within software development. The conferences are held each year in many places such as Oslo, Copenhagen, London, Sydney and Minnesota.

Update Conference Prague

Update Conference Prague is the biggest developer conference in the Czech Republic. The conference is offering sessions delivered by the top experts from all around the world. Their goal is to inspire the attendees and enrich their knowledge.

Troy Hunt

Learn about Web Security from Troy Hunt. He is a really engaged speaker that frequently give talks on conferences around the world. Troy is a Microsoft MVP and you can even learn from him on some great courses on Pluralsight.

W3Schools

W3Schools.com is a great education Web Site for learning web technologies. On W3Schools you may find well organized basic to advanced tutorials and references.

Scott Hanselman

Learn about Web Technologies and new trends from Scott Hanselman. Scott Hanselman is an author of developer books and he is an engaged speaker that usually talks about the Microsoft stack. You may meet Scott on conferences around the world.

Developer Week

DeveloperWeek is one of the world’s largest developer conferences. Developer Week focus on new dev technologies, the conference have talks and workshops for newbies and experienced audience. You can attend on a Developer Week conference different places in Nothern America.


BACK TO TOP

Honneybag blog



Learn JavaScript Debugging

Searching for bugs and fixing them is called code debugging. The bugs might be difficult to diagnose and therefore it is important to have a good approach to find and fix the bugs effectively. Bugs in the code might be syntax errors or logical errors. Sometimes nothing happens when the code contains bugs and there is few indications where to search. Modern web browser includes a powerful suite of developer tools. The tools do a range of things...

Explore JavaScript Arrays

Arrays are frequently used by developers. Programming languages can have slightly different implementation of arrays. An array is an object that can store a collection of items. You may say it`s a special variable that can have more than one value. The array holds many values under a single name, and you may access the values by referring to an index number. The easiest way to create....

Ultimate Guide to HTML Colors

It is essential to give the user a good user experience. There are many things you should focus on, one of them is how you use colors on your website. We don't have to struggle with black and white TVs anymore. Users expect more and more and we can apply colors to everything we want. Texts, borders, backgrounds, shadows – in HTML they all can have whatever color you decide....

Wanna be a sheep? Check out the most popular subjects
HONNEYBAG BLOG
JAVASCRIPT ESSENTIALS
HTML FORMATTING
HONNEYBAGBLOG INSPIRE-AND-BE-INSPIRED
HONNEYBAGBLOG EXPLORE-JAVASCRIPT-ARRAYS
Wanna be a little different? Check out the less popular subjects
JAVASCRIPT BREAKER
HTML COMMENTS
HTML BUILDING-BLOCKS
HTML COMPUTER-CODE
HTML API-GEOLOCATION
BACK TO TOP