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JavaScript is undoubtedly a language for both front-end and back-end developers. It is touted as the web language because over 90% of websites use JavaScript in one way or another.

If you are just getting started with JavaScript, you must have written functions, used simple algorithms, or worked with classes. However, as you progress in your career, you will realize that modern JavaScript frameworks like Node.js can extend the application of JavaScript to the backend. Learning advanced JavaScript concepts will help optimize the speed and performance of applications. You can move ahead from using jQuery for each functionality in the web application that makes it load slower.

Here are the must-learn JavaScript concepts that every front-end developer must know:

1. Let and Const Keywords

In its early days, JavaScript only supported var keywords for declaring variables. However, it limited the scope of the language as it only allowed variables to be global or functional. Also, variables declared with var can be re-declared and even updated. This makes it unsafe to use for security features and applications. 

JavaScript offers two new keywords to overcome these challenges – Let and Const. 

Variables with these keywords have block scopes. Moreover, let variables cannot be re-declared. But they can be updated. While the variable declared with const can neither be re-declared nor be updated. 

New JavaScript developers must learn the concept of let and const keyword variable declaration to write more optimized code. 

2. Closures

A closure is a function created inside another function but has access to the outer function variables. While the definition might seem straightforward, the closure is an excellent feature for making JavaScript code more cohesive. As the closures can access the variable defined within its scope, in the range of their parent functions, and the global variables, you can extend the behavior of an external function to the inner function. 

Being an essential object-oriented programming (OOP) concept, it makes JavaScript a highly scalable and high-performance language for front-end development. 

Here’s an example:

function init() {
var name = ‘Mozilla’; // name is a local variable created by init
function displayName() { // displayName() is the inner function, a closure
alert(name); // use variable declared in the parent function
}
displayName();
}
init();

Code with Closure: 

function makeFunc() {
var name = ‘Mozilla’;
function displayName() {
alert(name);
}
return displayName;
}
var myFunc = makeFunc();
myFunc();

Both the codes will have the same output, but in the second code, the displayName() inner function is returned from the outer function before being executed.

3. String Interpolation

In any programming language, strings are the most widely used data types. But, in JavaScript, strings are excessively used because front-end features like forms and logins have many string values. However, working with strings can be complicated when you have many inputs. For example, consider this code block:

let firstname = “Sarah”;
let secondname = “Connor”;

let age = 22;

let location = “Boston”;

return firstname + ” ” + secondname + ” is ” + age + ” years old and he lives in ” + city;

While there is no problem with the output string, and it will work just fine, the use of so many unique characters makes it somewhat complex.

String interpolation makes it a lot easier to handle such strings. The same output can be returned without any concatenation operators using string interpolation, as follows:

return `${firstname} ${secondname} is ${age} years old and he lives in ${city}`;

This concept makes it easier to work with strings. Furthermore, it is one of the most asked JavaScript interview questions.

4. Callbacks

In JavaScript, Callbacks are functions that are passed to other functions as parameters. They are invoked or executed inside other functions in serial formation, where one function waits for another to complete. As JavaScript is used to create asynchronous operations, Callbacks help to provide the synchronous capability to these operations.

Example: 

function myDisplayer(some) {
document.getElementById(“demo”).innerHTML = some;
}

function myCalculator(num1, num2, myCallback) {
let sum = num1 + num2;
myCallback(sum);
}

myCalculator(5, 5, myDisplayer);

This example myDisplayer is a function passed to myCalculator() as an argument.

5. Arrow function

The arrow function is another important concept for JavaScript developers to master. It is a simple concept that enables developers to write functions succinctly. Let’s understand with an example.

function demo(a, b) {
return a + b;
}

The demo function is created using the traditional “function” keyword here. Now we make the same JavaScript function using the arrow function.

const demo = (a,b) => a + b;

The output will be the same. When a function has a single statement, we can omit the “return” keyword with arrow function.

Another reason to learn arrow function is that they are essential for functional programming in JavaScript. To know the advanced use of these functions, you can take the Udemy Advanced JavaScript Concepts course.

Conclusion

The JavaScript features listed above are easy to understand and can make your code much more functional. Due to its asynchronous structure, JavaScript code can get complex to write and debug as the size of the application grows. These concepts will help you write clean, concise, and maintainable JavaScript code at scale.

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