Just Learn Code

Mastering the Const Keyword: Understanding Its Usage and Differences from Let

Introduction to JavaScript const keyword

If you’re a JavaScript programmer, you’ve probably used the const keyword once or twice. But do you really understand what makes it different from the let keyword?

In this article, we’ll cover everything you need to know about the const keyword and how it differs from let, with a focus on its usage with objects.

Explanation of const keyword

In JavaScript, const is a keyword that is used to declare read-only variables. This means that once a value has been assigned to a const variable, it cannot be reassigned.

It is important to note that const variables are not constants, they just have a constant value.

Convention for constant identifier

It’s a convention in JavaScript to use all uppercase letters when declaring a constant identifier. This makes it easier to distinguish a constant variable from a regular one and to remember not to reassign its value.

Differences between const keyword and let keyword

One of the main differences between the const and let keywords is that const variables are blocked-scoped, while let variables are function-scoped. This means that const variables can only be accessed within the block in which they were declared, while let variables can be accessed within the entire function.

Another difference is that const variables are immutable, while let variables are mutable. This means that while you can reassign the value of a let variable, trying to reassign the value of a const variable will result in a TypeError.

Initialization requirement for const keyword

When declaring a const variable, you must initialize it with a value. Failure to do so will result in a SyntaxError.

JavaScript const and Objects

Immutable value of const variable

When you declare a const variable that is an object, the variable itself is immutable, but the properties of the object are not necessarily immutable. This means that you can’t reassign the variable to a different object, but you can still modify the properties of the object.

Freezing object using Object.freeze() method

If you want to create an object that is completely immutable, you can use the Object.freeze() method. This method makes the object and all its properties immutable, which is also known as a shallow freeze.

However, it’s important to note that if the object contains nested objects, those nested objects are not frozen.

Example of constant and frozen object

Let’s take a look at an example of a constant object and a frozen object:

const myObject = {

name: “John”,

age: 30

};

Object.freeze(myObject);

In this example, the myObject object is declared as a const, which means that you can’t reassign it to a different object. However, you can still modify its properties.

If you want to make the object and all its properties immutable, you can use the Object.freeze() method, which will create a frozen object.

Conclusion

In conclusion, the const keyword in JavaScript is used to declare read-only variables that cannot be reassigned once they have been initialized. When using const with objects, the object itself is immutable, but its properties may not be.

To create an object that is completely immutable, you can use the Object.freeze() method. By understanding these concepts, you can write more efficient and reliable code in JavaScript.

JavaScript const and Arrays

In addition to working with objects, the const keyword in JavaScript can also be used with arrays. However, because arrays are mutable, the const keyword behaves differently when used with arrays than it does with objects.

Example of changing array elements using const keyword

Let’s take a look at an example:

const myArray = [1, 2, 3];

myArray.push(4);

console.log(myArray);

In this example, we initialize a const variable myArray with an array containing the values 1, 2, and 3. Despite being declared as const, we can still modify the array by calling the push() method to add the value 4 to the end of the array.

When we log the array to the console, we get the values [1, 2, 3, 4]. However, if we try to reassign the variable to a new array, like this:

myArray = [5, 6, 7];

We’ll get a TypeError, because we’re trying to reassign a value to a const variable.

JavaScript const in a for loopto for…of loop

In JavaScript, the for…of loop is used to iterate over iterable objects, like arrays and strings. It is similar to the for loop, but is more concise and easier to read.

Here’s an example:

const myArray = [1, 2, 3];

for (const element of myArray) {

console.log(element);

}

In this example, we use the for…of loop to iterate over the elements in the myArray array. The const keyword is used to create a new binding for the element variable, which is assigned each element in the array in turn.

Creating new binding for const keyword using for…of loop

One of the benefits of using the for…of loop is that it allows us to create a new binding for the const keyword with each iteration of the loop. This means that we can modify the value of the variable within the loop without affecting the original array.

Let’s take a look at another example:

const myArray = [1, 2, 3];

for (const element of myArray) {

element = element + 1;

console.log(element);

}

In this example, we use the for…of loop to iterate over the elements in the myArray array. However, when we try to modify the value of element by adding 1 to it, we get a TypeError, because the variable is declared as const.

To modify the value of an element in the array, we need to use the index of the element instead:

const myArray = [1, 2, 3];

for (let i = 0; i < myArray.length; i++) {

myArray[i] = myArray[i] + 1;

console.log(myArray[i]);

}

In this example, we use an imperative for loop to iterate over the elements in the myArray array. Because we use the let keyword to declare the i variable, we can modify the elements in the array by using the index i to access them.

TypeError when using const keyword in imperative for loop

If we try to use the const keyword in an imperative for loop to modify the value of an element in an array, like this:

const myArray = [1, 2, 3];

for (const i = 0; i < myArray.length; i++) {

myArray[i] = myArray[i] + 1;

console.log(myArray[i]);

}

We’ll get a TypeError, because we’re trying to modify a const variable. In this case, we need to use the let keyword to create a new binding for the i variable that can be modified within the loop.

Conclusion

The const keyword in JavaScript is a powerful tool that can help you write more efficient and reliable code. When used with objects, it makes the object itself immutable, but not necessarily its properties.

When used with arrays, it allows us to modify the array’s elements, but not reassign the variable to a new array. By understanding how the const keyword works with different data types and looping constructs, you can make the most of its features in your JavaScript projects.

Summary of JavaScript const keyword

The const keyword in JavaScript is a powerful tool that helps ensure data remains constant throughout program execution. When used with objects and arrays, it determines whether certain values can be adjusted or remain immutable.

In addition to this, the const keyword also allows for read-only references to data, utilizing blocked-scope coding structures that differ greatly from the mutable quality of the let keyword. Exploration of Read-Only References & Blocked-Scope Syntax

A primary characteristic of the const keyword in JavaScript is that it allows for the creation of read-only references.

A read-only reference is essentially a pointer that allows access to certain data stored within a program. Unlike mutable data, which can be altered and manipulated throughout the program, read-only data is locked in place, nonmodifiable, and can be used throughout the program without fear of changes.

Blocked-scope syntax is another fundamental aspect that distinguishes the const keyword from the let keyword. Blocked-scoped data is locked into code blocks, which means that it cannot be accessed or manipulated outside of the present code block.

This type of syntax is especially useful when programming large or pointed projects, as it allows developers to keep certain data structures isolated without fear of outside interference. Differences Between Const & Let Keywords

The const and let keywords in JavaScript are both integral elements of the coding system, and while they may overlap in some areas, they vary significantly in other important scopes.

There are three major differences between the const and let keywords in JavaScript: immutability, mutual exclusivity, and redeclaration. One of the most obvious differences between the two keywords is immutability.

While let keyword data can be modified and manipulated throughout the code, data marked by the const keyword is immutable, meaning it cannot be altered by any code structure. This quality makes the const keyword appealing when dealing with data that must remain the same throughout the program and guarantees greater reliability and consistency of the data.

The mutual exclusivity of the const and let keywords is another important distinction between the two. The const keyword allows the establishment of a read-only reference, creating a pointer to specific data within the program that cannot be changed.

In contrast, the let keyword creates mutable data, allowing it to be altered by the program throughout the execution. While the two keywords can be used in the same project, they are exclusive to different types of data and program structures.

Finally, redeclaration is another significant point of difference between the const and let keywords. Redeclaration, the act of establishing multiple values or pointers to the same data, is possible in the let keyword format, but impossible using the const keyword.

This quality of the const keyword prevents the programmer from accidentally reassigning a value to potential accidental changes, providing important stability when working with complex programs.

Conclusion

JavaScript’s const keyword is an essential tool for programming reliable and stable code, allowing developers to maintain nonmodifiable data types that remain constant throughout program execution. Its syntax is divided into blocked-scoped structure, which allows for great automation without fear of interference.

While the const and let keywords may appear similar, it is critical to understand the differences between the two and their particular applicability in their program structures. In conclusion, the const keyword in JavaScript is a powerful tool that ensures data remains constant throughout program execution and allows for read-only references to data.

Its blocked-scope syntax provides an extra level of protection against interference that is especially useful in larger projects. Understanding the differences between the const and let keywords is crucial to creating reliable and stable code, and it is vital in choosing the appropriate keyword for specific data types and program structures.

By learning and utilizing the unique features of the const keyword, you can enhance the reliability, efficiency, and safety of your JavaScript projects.

Popular Posts