## Introduction

In this tutorial, we will learn how to build a calculator using JavaScript. A calculator is a useful tool that allows users to perform calculations quickly and easily. By building our own calculator with JavaScript, we can customize it to suit our specific needs and preferences. Additionally, creating a calculator with JavaScript is a great way to practice our coding skills and gain a better understanding of how JavaScript works in a real-world application. So, let's get started and learn how to build our very own calculator!

## Prerequisites

To build a calculator with Javascript, you should have a basic knowledge of HTML, CSS, and Javascript. Understanding these languages will help you create and manipulate the necessary elements on the web page. Additionally, you will need a text editor or integrated development environment (IDE) installed on your computer to write and run the code. This will allow you to easily edit and test your calculator project.

## Getting Started

To get started with building a calculator using Javascript, you will need to set up an HTML file. Open a text editor or IDE and create a new HTML file. You can name it whatever you like.

In the HTML file, you will need to create the necessary elements for the calculator. This includes an input box where the user can enter numbers and operators, and buttons for the different arithmetic operations.

To create the input box, use the `<input>`

tag with the type attribute set to "text". This will create a text input field where the user can enter numbers and operators.

<input type="text" id="calculator-input">

Next, you will need to create the buttons for the arithmetic operations. You can use `<button>`

tags for this purpose. Give each button a unique id and set the text inside the button to the corresponding arithmetic operation.

<button id="addition">+</button> <button id="subtraction">-</button> <button id="multiplication">*</button> <button id="division">/</button>

With these elements in place, you have set up the basic structure of the calculator. In the next section, we will add functionality to the calculator using Javascript.

## Adding Functionality

To make the calculator functional, we need to add event listeners to the buttons and create functions for the basic arithmetic operations.

First, we need to add event listeners to the buttons in order to capture user input. This can be done using JavaScript's `addEventListener`

method. By attaching an event listener to each button, we can detect when a button is clicked and trigger a corresponding function.

Next, we need to create functions for the basic arithmetic operations: addition, subtraction, multiplication, and division. These functions will take the entered numbers as input and perform the respective operation. We can use JavaScript's built-in arithmetic operators to perform these calculations.

By combining event listeners with these arithmetic functions, we can create a calculator that performs calculations based on user input.

## Addition

In order to handle addition in our calculator, we need to create a function that takes two numbers as input and returns their sum.

Here is an example code snippet that demonstrates how to implement the addition function in Javascript:

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

In this code, the `add`

function takes two parameters `a`

and `b`

, representing the numbers to be added. The function then uses the `+`

operator to perform the addition and returns the result.

To use this function in our calculator, we can call it whenever the user clicks the addition button. We can pass the numbers entered by the user as arguments to the `add`

function and display the result on the calculator display.

By following this approach, our calculator will be able to perform addition operations accurately and display the correct result to the user.

## Subtraction

To handle subtraction in our calculator, we need to create a function that takes two numbers as input and returns the result of subtracting the second number from the first number.

Here is an example code snippet that demonstrates how to implement the subtraction function:

function subtract(a, b) { return a - b; }

In this example, the function `subtract`

takes two parameters, `a`

and `b`

, which represent the numbers to be subtracted. The function subtracts `b`

from `a`

and returns the result.

To use the subtraction function, you can call it with the desired numbers as arguments. For example:

let result = subtract(10, 5); console.log(result); // Output: 5

In this example, we call the `subtract`

function with the numbers 10 and 5. The function subtracts 5 from 10 and returns the result, which is then stored in the variable `result`

. Finally, we log the result to the console.

By implementing this subtraction function in our calculator, we can easily handle subtraction operations and display the results to the user.

## Multiplication

To handle multiplication in our calculator, we need to create a function that takes two numbers as inputs and returns their product. We can then use this function to perform the multiplication operation when the user clicks on the multiplication button.

Here is an example code snippet that demonstrates how to implement the multiplication function in Javascript:

function multiply(num1, num2) { return num1 * num2; }

In this code, the `multiply`

function takes two parameters `num1`

and `num2`

, representing the numbers to be multiplied. The function uses the `*`

operator to multiply the two numbers and returns the result.

To use this function in our calculator, we can add an event listener to the multiplication button and call the `multiply`

function with the appropriate inputs. The result can then be displayed on the calculator's display.

const multiplicationButton = document.getElementById('multiplication-button'); multiplicationButton.addEventListener('click', function() { const num1 = parseFloat(document.getElementById('num1').value); const num2 = parseFloat(document.getElementById('num2').value); const result = multiply(num1, num2); document.getElementById('result').innerText = result; });

In this code, we first retrieve the values entered by the user for `num1`

and `num2`

from the input fields. We then call the `multiply`

function with these values and store the result in the `result`

variable. Finally, we update the calculator's display with the result.

By following these steps, we have successfully implemented the multiplication functionality in our calculator. The same approach can be used to handle other arithmetic operations as well.

## Division

To handle division in our calculator, we need to create a function that performs the division operation. We can use the built-in division operator (/) in JavaScript to divide two numbers.

Here's an example code snippet that demonstrates how to handle division in our calculator:

function divide() { // Get the values from the input box var num1 = parseFloat(document.getElementById("num1").value); var num2 = parseFloat(document.getElementById("num2").value); // Perform the division operation var result = num1 / num2; // Display the result on the calculator display document.getElementById("result").textContent = result; }

In this code snippet, we define a function called `divide()`

that retrieves the values entered by the user from the input box. We use the `parseFloat()`

function to convert the input values from strings to numbers.

Next, we perform the division operation by dividing `num1`

by `num2`

, and store the result in a variable called `result`

.

Finally, we update the calculator display by setting the `textContent`

property of the element with the id "result" to the value of `result`

.

By calling this `divide()`

function when the corresponding button is clicked, we can perform division in our calculator.

## Handling User Input

When building a calculator with JavaScript, it is important to handle user input correctly. This involves storing the numbers entered by the user and handling decimal input.

To store the numbers entered by the user, we can create a variable to keep track of the current number. Whenever a user clicks a number button, we can update this variable by concatenating the clicked number to the current number. For example, if the user clicks the buttons '1', '2', and '3', the current number would be '123'.

Handling decimal input requires some extra logic. We need to ensure that there is only one decimal point in the current number. We can do this by checking if the current number already contains a decimal point before adding another one. If it does, we can ignore the new decimal point input. This prevents the user from entering invalid numbers with multiple decimal points.

By implementing these techniques, we can effectively handle user input in our calculator and ensure that the numbers entered are stored correctly.

## Displaying the Result

To display the result of the calculations on our calculator, we need to update the calculator display. This display can be an input box or a text element on our HTML page.

When an operation is performed, we can store the result in a variable. Then, we can update the value of the display element with the result using JavaScript. This can be done by accessing the element using its id and setting its value property to the result.

For example, if our display element has an id of "result", we can update it like this:

document.getElementById("result").value = result;

Where `result`

is the variable that holds the calculated result.

In addition to updating the display, it is also important to provide a way to clear the display when needed. This can be done by assigning an event listener to a "clear" button, which will reset the display to its initial state. The event listener can be added using JavaScript, and the code inside the listener function can set the value of the display element to an empty string.

For example, if our clear button has an id of "clearBtn", we can add the event listener like this:

document.getElementById("clearBtn").addEventListener("click", function() { document.getElementById("result").value = ""; });

This code assigns an anonymous function as the event handler for the "click" event of the clear button. Inside this function, we set the value of the display element to an empty string, effectively clearing the display.

By updating the display with the result of the calculations and providing a way to clear it, our calculator becomes more user-friendly and intuitive.

## Conclusion

In this tutorial, we have learned how to build a calculator with Javascript. We started by setting up the HTML file and creating the necessary elements for our calculator, including an input box and buttons.

Next, we added functionality to our calculator by adding event listeners to the buttons and creating functions for the basic arithmetic operations such as addition, subtraction, multiplication, and division. Each operation was handled using a separate function, and we provided example code snippets and explanations for each.

We also learned how to handle user input by storing the numbers entered by the user and handling decimal input. This ensured that our calculator could handle both whole numbers and decimals.

Finally, we discussed how to display the result on the calculator and provided code examples for updating the display and clearing it when needed.

Now that you have learned how to build a calculator with Javascript, I encourage you to practice and explore further. You can add more advanced functionality to your calculator, such as handling parentheses or adding more complex operations. Keep experimenting and building on what you have learned to enhance your skills as a Javascript developer. Happy coding!