Listening to events for this situation

Question

Listening to events for this situation

As a beginner in JavaScript, I have been studying event listeners and how to apply them to my code. I am currently working on a basic calculator project where users input two amounts into HTML fields for addition. Although my current code functions correctly, it does not update the total amount when the field values change. This is why I believe I need an event listener. Can you guide me on how to implement this in my scenario? I have reviewed online examples but still struggle with the concept.

Should I incorporate some of my code within a function?

Note: It's important that my global variable "paytotal" always displays the most up-to-date results so I can access this data across my page.

Below is my existing JavaScript:

var payamount1 = document.getElementById("amount1").value;
var payamount2 = document.getElementById("amount2").value;
var paytotal = Number(payamount1) + Number(payamount2);
document.getElementById("payment-due").innerHTML = paytotal;

This is what my HTML looks like:

<input type="text" id="amount1" placeholder="enter amount 1">
<input type="text" id="amount2" placeholder="enter amount 2">

<div class="details-row">Total payable: <span id="payment-due"></span></div>

javascript

Answer 1

Answer №1

Event listeners are designed to detect when a specific action occurs. In this scenario, the ideal event to listen for is 'input' as it captures all necessary changes.

To simplify the process, assigning a class to your inputs would be beneficial.

The following JavaScript code will apply an input listener to the assigned input elements:

var amounts = document.querySelectorAll(".amounts");
var paytotal = 0;
amounts.forEach(function(el){
  el.addEventListener("input",function(){
   var payamount1 = document.getElementById("amount1").value;
   var payamount2 = document.getElementById("amount2").value;
    paytotal = Number(payamount1) + Number(payamount2);
   document.getElementById("payment-due").innerHTML = paytotal;
});
});

<input class="amounts" type="text" id="amount1" placeholder="enter amount 1">
<input class="amounts" type="text" id="amount2" placeholder="enter amount 2">

<div id="payment-due"></div>

Answer 2

Event listeners are designed to detect when a specific action occurs. In this scenario, the ideal event to listen for is 'input' as it captures all necessary changes.

To simplify the process, assigning a class to your inputs would be beneficial.

The following JavaScript code will apply an input listener to the assigned input elements:

var amounts = document.querySelectorAll(".amounts");
var paytotal = 0;
amounts.forEach(function(el){
  el.addEventListener("input",function(){
   var payamount1 = document.getElementById("amount1").value;
   var payamount2 = document.getElementById("amount2").value;
    paytotal = Number(payamount1) + Number(payamount2);
   document.getElementById("payment-due").innerHTML = paytotal;
});
});

<input class="amounts" type="text" id="amount1" placeholder="enter amount 1">
<input class="amounts" type="text" id="amount2" placeholder="enter amount 2">

<div id="payment-due"></div>

Answer 3

Answer №2

To enhance functionality, add an event listener to each input field triggering a function (calc) that contains your custom code.

var amount1 = document.getElementById("amount1");
var amount2 = document.getElementById("amount2")
amount1.addEventListener('change', calc);
amount2.addEventListener('change', calc);

function calc() {
    var payamount1 = amount1.value;
    var payamount2 = amount2.value;
    var paytotal = Number(payamount1) + Number(payamount2);
    
    document.getElementById("payment-due").innerHTML = paytotal;
}

<input type="text" id="amount1" placeholder="enter amount 1">
<input type="text" id="amount2" placeholder="enter amount 2">
<div class="details-row">Total payable: <span id="payment-due"></span></div>

Answer 4

To enhance functionality, add an event listener to each input field triggering a function (calc) that contains your custom code.

var amount1 = document.getElementById("amount1");
var amount2 = document.getElementById("amount2")
amount1.addEventListener('change', calc);
amount2.addEventListener('change', calc);

function calc() {
    var payamount1 = amount1.value;
    var payamount2 = amount2.value;
    var paytotal = Number(payamount1) + Number(payamount2);
    
    document.getElementById("payment-due").innerHTML = paytotal;
}

<input type="text" id="amount1" placeholder="enter amount 1">
<input type="text" id="amount2" placeholder="enter amount 2">
<div class="details-row">Total payable: <span id="payment-due"></span></div>

Answer 5

Answer №3

There are numerous ways to achieve this task. Here is one method; Ensure to validate that the result is not NaN

function calculateTotal() {


  var inputValue1 = document.getElementById("value1").value;
  var inputValue2 = document.getElementById("value2").value;

  if (inputValue1 != '' && inputValue2 != '') {
    var totalValue = Number(inputValue1) + Number(inputValue2);
    
    if(!Number.isNaN(totalValue))document.getElementById("result-display").innerHTML = totalValue;
  }

}

<input type="text" id="value1" placeholder="enter value 1" onchange="calculateTotal()">
<input type="text" id="value2" placeholder="enter value 2" onchange="calculateTotal()">
<div class="details-area">Total amount: <span id="result-display"></span></div>

Answer 6

There are numerous ways to achieve this task. Here is one method; Ensure to validate that the result is not NaN

function calculateTotal() {


  var inputValue1 = document.getElementById("value1").value;
  var inputValue2 = document.getElementById("value2").value;

  if (inputValue1 != '' && inputValue2 != '') {
    var totalValue = Number(inputValue1) + Number(inputValue2);
    
    if(!Number.isNaN(totalValue))document.getElementById("result-display").innerHTML = totalValue;
  }

}

<input type="text" id="value1" placeholder="enter value 1" onchange="calculateTotal()">
<input type="text" id="value2" placeholder="enter value 2" onchange="calculateTotal()">
<div class="details-area">Total amount: <span id="result-display"></span></div>

Listening to events for this situation

Answer №1

Answer №2

Answer №3

Similar questions

Creating a sleek animated analog clock using CSS and jQuery

What is the method for modifying the background color of the inner circle in a highchart doughnut chart?

Combining and overriding two JavaScript objects in real time

Exploring the wonders of math in Angular with ng-repeat

Initiate a series of tasks and await their completion using RxJS / Redux Observables

The AngularJs project is currently experiencing issues when trying to function as a single page web application

Retrieve data from FileReader's onload event asynchronously in Javascript

Using jQuery to display items from GitHub API in a custom unordered list format

Having trouble with Selenium WebDriverJS on both FireFox and Internet Explorer

How to automatically generate a serial number using JavaScript each time a click event occurs

Describe a Typescript Interface Value as a collection of strings or any input provided as an argument

Transform the JSON object into a TypeScript array

What is the procedure for verifying the type of an element using chai?

What is the way to utilize a scope variable within an ng-repeat filter?

Creating packaging for a node-webkit application

"Create a function that allows for the dynamic addition of elements to a

Leveraging the useRef hook to adjust the CSS styling of a React component

JavaScript and CSS Modal showing incorrect data

Updating the state on a click event triggered by a MenuItem in React using Material UI

What is the proper way to connect an external Javascript file to an html document within a Play Framework project?