Develop Reference

JavaScript array application

I'm trying to create a sample accounting system, the checkbox can be add to the total after it's checked and the input text is the amount of the money.
but my result keep getting zero, I can't figure it out.
Anyone can help me handle this problem?
I've test that the length of total_ary is 0, I think that is the mainly problem
function Totalamount() {
var input_cb = document.getElementsByName('cb');
var amount = [];
var total_ary = [];
var total = 0;
var price = [10, 20, 30];
var i = 0;
for (i = 0; i < input_cb.length; i++) {
if (input_cb[i].checked) {
amount.push(document.getElementsByName("amount").value); //get amounts of the products
} else {
amount.push(0); //If there is no input, add 0 to the array
}
}
for (i = 0; i < total_ary.length; i++) {
total_ary.push(parseInt(amount[i] * price[i])); // Add the products' total price to array
total += parseInt(total_ary[i]); //Counting the total money
}
document.getElementById("result").innerHTML = "$" + 0;
document.getElementById("result").innerHTML = "$" + total ;
}
<fieldset>
<input type="checkbox" name="cb" checked>$10：<input type="text" name="amount"><br>
<input type="checkbox" name="cb" checked>$20：<input type="text" name="amount"><br>
<input type="checkbox" name="cb" checked>$30：<input type="text" name="amount"><br>
</fieldset>
<button onclick="Totalamount()">Count</button>
<p>Total = <span id="result">

You do
document.getElementsByName("amount").value
but getElementsByName returns a collection, not an element.
You do
var total_ary = [];
// ... code that doesn't reference total_ary
for (i = 0; i < total_ary.length; i++) {
total_ary.push(parseInt(amount[i] * price[i])); // Add the products' total price to array
total += parseInt(total_ary[i]); //Counting the total money
}
But since the code in between doesn't reference total_ary, the total ends up being 0.
From a selected checkbox, you need to navigate to the associated input:
document.getElementsByName("amount")[i].value
since i is the cb index you're iterating over, the same i in the amount collection will refer to the input you need.
Or, more elegantly, just navigate to the next element in the DOM when a checkbox is checked, and take the number for each product's price from the DOM too. You can also select only the checked checkboxes immediately with a :checked selector, and attach the event listener using addEventListener (instead of an inline handler; inline handlers should be avoided)
document.querySelector('button').addEventListener('click', () => {
let total = 0;
for (const input of document.querySelectorAll('[name=cb]:checked')) {
const price = input.nextSibling.textContent.match(/\d+/)[0];
const amount = input.nextElementSibling.value;
total += price * amount;
}
document.getElementById("result").innerHTML = total + "元";
});
<fieldset>
<input type="checkbox" name="cb" checked>$10：<input><br>
<input type="checkbox" name="cb" checked>$20：<input><br>
<input type="checkbox" name="cb" checked>$30：<input><br>
</fieldset>
<button>Count</button>
<p>Total = <span id="result">

document.getElementsByName() returns a collection of elements. so calling value property will not work there as it does not have such property.
You can hold input elements with amount_inputs variable and iterate over it (in the example below by using spread syntax and Array.reduce())
And with Array.reduce() you can calculate the sum of the prices. There is no need for var amount = [] and var total_ary = [] variables.
Hope this helps
function Totalamount() {
var input_cb = document.getElementsByName('cb');
var amount_inputs = document.getElementsByName("amount")
var total = 0;
var price = [10, 20, 30];
total = [...input_cb].reduce((total, cb, i) => {
if(cb.checked){
total += (parseInt(amount_inputs[i].value) || 0) * price[i]
// ^^^^^^^^^ This is to avoid NaN multiplication
}
return total
},0);
document.getElementById("result").innerHTML = "$" + 0;
document.getElementById("result").innerHTML = total + "元";
}
<fieldset>
<input type="checkbox" name="cb" checked>$10：<input type="text" name="amount"><br>
<input type="checkbox" name="cb" checked>$20：<input type="text" name="amount"><br>
<input type="checkbox" name="cb" checked>$30：<input type="text" name="amount"><br>
</fieldset>
<button onclick="Totalamount()">Count</button>
<p>Total = <span id="result">

Use Index while retrieving the element from document.getElementsByName("amount");
Use for loop on amount array not on total_ary
function Totalamount() {
var input_cb = document.getElementsByName('cb');
var amount = [];
var total_ary = [];
var total = 0;
var price = [10, 20, 30];
var i = 0;
for (i = 0; i < input_cb.length; i++) {
if (input_cb[i].checked) {
amount.push(document.getElementsByName("amount")[i].value); //get amounts of the products
} else {
amount.push(0); //If there is no input, add 0 to the array
}
}
for (i = 0; i < amount.length; i++) {
total_ary.push(parseInt(amount[i] * price[i])); // Add the products' total price to array
total += isNaN(parseInt(total_ary[i])) ? 0 : parseInt(total_ary[i]); //Counting the total money
}
document.getElementById("result").innerHTML = "$" + 0;
document.getElementById("result").innerHTML = "$" + total ;
}
<fieldset>
<input type="checkbox" name="cb" checked>$10：<input type="text" name="amount"><br>
<input type="checkbox" name="cb" checked>$20：<input type="text" name="amount"><br>
<input type="checkbox" name="cb" checked>$30：<input type="text" name="amount"><br>
</fieldset>
<button onclick="Totalamount()">Count</button>
<p>Total = <span id="result">

You have made a few mistakes:
(1) If you want to keep all the checkboxes checked at initial stage
use checked="true" in place of checked
(2) getElementsByName("amount") returns an array, so you should use the index as well
(3) total_ary length is 0 initially.. therefore, you should run the loop with input_cb. (Here, you can do both the task with a single loop: refer code below)
Refer the code with corrections:
<!DOCTYPE html>
<html>
<head>Order sys
<script>
function Totalamount() {
var input_cb = document.getElementsByName('cb');
var amount = [];
var total = 0;
var price = [10,20,30];
var i=0;
for (i = 0; i < input_cb.length; i++) {
if (input_cb[i].checked){
amount.push(parseInt(document.getElementsByName("amount")[i].value)); //get amounts of the products
}
else{
amount.push(0); //If there is no input, add 0 to the array
}
total += parseInt(amount[i] * price[i]) //Counting the total money
}
document.getElementById("result").innerHTML = "$" + 0;
document.getElementById("result").innerHTML = total + "元";
}
</script>
</head>
<body>
<fieldset>
<input type = "checkbox" name="cb" checked="true">$10：<input type="text" id="amount_milk" name="amount" ><br>
<input type = "checkbox" name="cb" checked="true">$20：<input type="text" id="amount_soymlik" name="amount"><br>
<input type = "checkbox" name="cb" checked="true">$30：<input type="text" id="amount_blacktea" name="amount" ><br>
</fieldset>
<button onclick="Totalamount()">Count</button>
<p>Total = <span id="result">
</body>
</html>

You can refactor your code:
Fist use inputs of type number <input type="number" name="amount"> to accept only numbers from your end users
Then, you can work with indexed arrays like [...document.querySelectorAll('input[name="cb"]')] and loop only one time with Array.prototype.reduce() to get the total
Code example:
function Totalamount() {
const inputNumberArr = [...document.querySelectorAll('input[name="cb"]')]
const inputAmountArr = [...document.querySelectorAll('input[name="amount"]')]
const priceArr = [10, 20, 30]
const total = inputNumberArr.reduce((a, c, i) => {
const num = c.checked ? +inputAmountArr[i].value : 0
return a + num * priceArr[i]
}, 0)
document.getElementById('result').innerHTML = '$' + 0
document.getElementById('result').innerHTML = '$' + total
}
<fieldset>
<input type="checkbox" name="cb" checked> $10：
<input type="number" name="amount"><br>
<input type="checkbox" name="cb" checked> $20：
<input type="number" name="amount"><br>
<input type="checkbox" name="cb" checked> $30：
<input type="number" name="amount"><br>
</fieldset>
<button onclick="Totalamount()">Count</button>
<p>Total = <span id="result">

Is this what you are looking for?
Errors that I identified.
Making use of document.getElementsByName("amount").value instead of making the respective amount field you were making use of the global selector.
Trying to loop total_ary array instead of amount array.
function Totalamount() {
var input_cb = document.getElementsByName('cb');
var amountInput = document.getElementsByName('amount');
var amount = [];
var total_ary = [];
var total = 0;
var price = [10,20,30];
var i=0;
for (i = 0; i < input_cb.length; i++) {
if (input_cb[i].checked && amountInput[i].value){
amount.push(parseInt(amountInput[i].value)); //get amounts of the products
}
else{
amount.push(0); //If there is no input, add 0 to the array
}
}
for (i = 0; i < amount.length; i++) {
total_ary.push(parseInt(amount[i] * price[i])); // Add the products' total price to array
total += parseInt(total_ary[i]); //Counting the total money
}
document.getElementById("result").innerHTML = "$" + 0;
document.getElementById("result").innerHTML = total + "元";
}
<fieldset>
<input type = "checkbox" name="cb" checked>$10
<input type="text" id="amount_milk" name="amount" ><br>
<input type = "checkbox" name="cb" checked>$20
<input type="text" id="amount_soymlik" name="amount"><br>
<input type = "checkbox" name="cb" checked>$30
<input type="text" id="amount_blacktea" name="amount" ><br>
</fieldset>
<button onclick="Totalamount()">Count</button>
<p>Total = <span id="result">

How to reuse code block in javascript

I am new to learning javascript and apologize if this question is too basic. I have tried to search for a solution but nothing has been clear to me. I have created this code in this link.
https://jsfiddle.net/5p7wzy9x/3/
var btn = document.getElementById("calc");
btn.addEventListener("click", function() {
var total = 0;
var count = 0;
var values = document.getElementsByClassName("value");
for (var i = 0; i < values.length; i++) {
var num = parseFloat(values[i].value);
if (!isNaN(num)) {
total += num;
count++;
}
}
output = total / count;
var totalTb = document.getElementById("total");
totalTb.value = count ? output : "NaN";
});
var btn = document.getElementById("calcTwo");
btn.addEventListener("click", function() {
var total = 0;
var count = 0;
var values = document.getElementsByClassName("value");
for (var i = 0; i < values.length; i++) {
var num = parseFloat(values[i].value);
if (!isNaN(num)) {
total += num;
count++;
}
}
output = (total / count);
var totalTb = document.getElementById("total");
totalTb.value = output >= 90 ? "A"
: output >= 80 ? "B"
: output >= 70 ? "C"
: output >= 60 ? "D"
: "YOU FAIL!";
});
My question is, how would I go about being able to use the same code for the second "grade" button without having to copy and pasting the same code?
I saw that you can use functions to invoke the same code block but am confused how I would go about it. I apologize if this question has already been answered, but I have diligently searched and tried to figure this out on my own. Thank you in advanced.

Instead of passing anonymous functions (functions with no names) to your event handlers as data:
btn.addEventListener("click", function() { ...
set up those functions as "function declarations" so that you can call them by name. Then, instead of passing them into the .addEventListner() method call, you reference them by name (without parenthesis next to the name).
Here's an example:
// Both buttons are configured to call the same event handling function:
document.getElementById("btn1").addEventListener("click", doSomething);
document.getElementById("btn2").addEventListener("click", doSomething);
function doSomething(){
console.log("Hello!");
}
<input type=button id="btn1" value="Click Me">
<input type=button id="btn2" value="Click Me">

Here is how you can combine common code in one function:
var btn = document.getElementById("calc");
var btn2 = document.getElementById("calcTwo");
var totalTb = document.getElementById("total");
btn.addEventListener("click", function() {
var output = getTotal();
totalTb.value = output < Infinity ? output : "NaN";
});
btn2.addEventListener("click", function() {
var output = getTotal();
totalTb.value = output >= 90 ? "A"
: output >= 80 ? "B"
: output >= 70 ? "C"
: output >= 60 ? "D"
: "YOU FAIL!";
});
function getTotal() {
var total = 0;
var count = 0;
var values = document.getElementsByClassName("value");
for (var i = 0; i < values.length; i++) {
var num = parseFloat(values[i].value);
if (!isNaN(num)) {
total += num;
count++;
}
}
output = total / count;
return output;
}
<form id="form1">
<input class="value" type="text" value="80" /><br />
<input class="value" type="text" value="50" /><br />
<input class="value" type="text" value="15" /><br />
<input class="value" type="text" value="30" /><br />
<input class="value" type="text" value="90" /><br />
<br />
<input type="text" id="total" />
<button type="button" id="calc">Calculate</button>
<button type="button" id="calcTwo">Grade</button>
</form>

Taking the sum of user inputs and storing it as a variable

What is the best way to calculate sum of user inputs from an array and then store that value as a variable?
I have a function here that creates an array from user inputs(number4[]).
var counter = 1;
var limit = 3;
function addInput(divName){
if (counter == limit) {
alert("You have reached the limit of adding " + counter + " inputs");
}
else {
var newdiv = document.createElement('div');
newdiv.innerHTML = "Asset($) " + (counter + 1) + " <br><input type='text' name='number4[]'>";
document.getElementById(divName).appendChild(newdiv);
counter++;
}
<div class="container7">
<div id ="dynamicInput">
Assets 1($): <INPUT type="text" name="number4[]">
</div>
Liabilities 1(%): <INPUT type="text" name="number5">
Result($): <INPUT type="text" name="total1">
<INPUT type="button" style="background-color:#FF8800; border-color:BLACK;" value="Calculate"onclick="javascript:networth()">
<INPUT type="button" style="background-color:#FF8800; border-color:BLACK;" value="Add asset fields"onclick="addInput('dynamicInput');">
</div>
</FORM>
I have no code for total1 yet. so basically i have the array i just need help identifying the sum and then assigning it as a variable.

document.getElementsByName("number4[]") will return an array of the elements you need to total up
function networth(){
var totNo = document.getElementsByName("number4[]").length;
var sum = 0;
for(var i=0; i<totNo; i++){
sum += parseInt(document.getElementsByName("number4[]")[i].value);
console.log(sum);
}
}

Add an id to your input elements and use
var val1 = document.getElementById("the id of the input you want").value
//repete for val2... with a different id and add the val variables

You need to get all the input elements you want to sum. You can use the querySelectorAll to get all the elements with a same CSS selector common in all the inputs you want to sum.
https://www.w3schools.com/jsref/met_document_queryselectorall.asp
Finally you can get the input in the same way with querySelector, as is only one there is no need to use the All variation.
https://www.w3schools.com/jsref/met_document_queryselector.asp
var counter = 1;
var limit = 3;
function networth(){
var inputs = document.querySelectorAll("form #dynamicInput input");
var networth = 0;
for (var i = 0; i < inputs.length; i++) {
networth += parseFloat(inputs[i].value);
}
document.querySelector("input[name=total1]").value=networth;
}
function addInput(divName) {
if (counter == limit) {
alert("You have reached the limit of adding " + counter + " inputs");
} else {
var newdiv = document.createElement('div');
newdiv.innerHTML = "Asset($) " + (counter + 1) +
" <br><input type='text' name='number4[]'>";
document.getElementById(divName).appendChild(newdiv);
counter++;
}
}
<form>
<div class="container7">
<div id="dynamicInput">
Assets 1($):<br>
<INPUT type="text" name="number4[]">
</div>
Liabilities 1(%):
<INPUT type="text" name="number5"> Result($):
<INPUT type="text" name="total1">
<INPUT type="button" style="background-color:#FF8800; border-color:BLACK;" value="Calculate" onclick="javascript:networth()" />
<INPUT type="button" style="background-color:#FF8800; border-color:BLACK;" value="Add asset fields" onclick="addInput('dynamicInput');" />
</div>
</FORM>

Unchecking a checkbox and modifying value of sum

I am trying to design a menu. If you check a box, then sum get added up and if you uncheck it, the sum is reduced. I face trouble in reducing the sum while unchecking the box and also the value of sum is not globally changed. Please help me out.
<head>
<script>
var sum=0;
function a(sum,num) {
sum=sum+num;
document.getElementById("demo").innerHTML=sum;
}
</script>
</head>
<body>
<input type="checkbox" name="Dal" id="dal" onclick=a(sum,10)>Dal<br>
<input type="checkbox" name="Rice" id="rice" onclick=a(sum,20)>Rice<br>
<h1> Total Price is : </h1>
<p id="demo"> 0 </p>
</body>

Change the markup, add a value and a class, and remove the inline JS
<input type="checkbox" name="Dal" id="dal" value="10" class="myClass">Dal
<input type="checkbox" name="Rice" id="rice" value="20" class="myClass">Rice
<h1> Total Price is : </h1><p id="demo">0</p>
Then do
<script type="text/javascript">
var inputs = document.getElementsByClassName('myClass'),
total = document.getElementById('demo');
for (var i=0; i < inputs.length; i++) {
inputs[i].onchange = function() {
var add = this.value * (this.checked ? 1 : -1);
total.innerHTML = parseFloat(total.innerHTML) + add
}
}
</script>
FIDDLE

You can do something like this:
function a (elem, num) {
var k = (elem.checked) ? 1 : -1;
sum = sum + k * num;
document.getElementById("demo").innerHTML = sum;
}
And in the HTML:
<input type="checkbox" name="Dal" id="dal" onclick="a(this, 10);">Dal<br>
<input type="checkbox" name="Rice" id="rice" onclick="a(this, 20);">Rice<br>

Try something like this:
var sum = 0;
function a(id, num) {
if(id.checked == true){
sum += num;
id.onclick = function() { a(id, num)};
}
else {
sum -= num;
id.onclick = function() { a(id, num)};
}
document.getElementById("demo").innerHTML=sum;
}
Fiddle: http://jsfiddle.net/95pvc/2/

My own take would involve removing the event-handling from the HTML (unobtrusive JavaScript) for easier maintenance in future, using data-* attributes to contain the price and using a class-name to identify the relevant ingredients, to give the following HTML:
<input class="ingredients" type="checkbox" name="Dal" data-price="10" id="dal" />Dal
<input class="ingredients" type="checkbox" name="Rice" data-price="20" id="rice" />Rice
<h1> Total Price is : </h1>
<p id="demo">0</p>
Which leads to the following JavaScript:
var ingredients = document.getElementsByClassName('ingredients');
function price() {
var result = document.getElementById('demo'),
curPrice = 0,
ingredients = document.getElementsByClassName('ingredients');
for (var i = 0, len = ingredients.length; i < len; i++) {
if (ingredients[i].checked) {
curPrice += parseFloat(ingredients[i].getAttribute('data-price'));
}
}
result.firstChild.nodeValue = curPrice;
}
for (var i = 0, len = ingredients.length; i < len; i++) {
ingredients[i].addEventListener('change', price);
}
JS Fiddle demo.
To avoid having to iterate through the relevant checkboxes, it might be better to wrap those input elements in a form, and then bind the event-handling to that form:
var ingredients = document.getElementsByClassName('ingredients');
function price() {
var result = document.getElementById('demo'),
curPrice = 0,
ingredients = document.getElementsByClassName('ingredients');
for (var i = 0, len = ingredients.length; i < len; i++) {
if (ingredients[i].checked) {
curPrice += parseFloat(ingredients[i].getAttribute('data-price'));
}
}
result.firstChild.nodeValue = curPrice;
}
document.getElementById('formID').addEventListener('change', price);
JS Fiddle demo.
References:
addEventListener().
element.getAttribute().
getElementsByClassName().
parseFloat().

JavaScript forms and functions

I am trying to write a simple random number generator, where you input 3 integers into forms. The program then returns a certain amount of random numbers between the other two values. When I open the page the forms are displayed but when I click the button to generate the random numbers nothing happens. Why is this happening?
<html>
<head>
<script LANGUAGE="JavaScript">
function randomFromTo(from, to)
{
return Math.floor(Math.random() * ((to - from) + 1) + from);
}
function include(arr, obj)
{
for(var j = 0; j < arr.length; j++)
{
if (arr[j] == obj) return true;
}
}
function RandomGen(form)
{
var enteries = new Array();
var number = form.from.value;
var top = form.top.value;
var size = form.inputBox.value;
var count;
for (count = 0; count < size; count++)
{
var num = randomFromTo(number, top);
if (include(enteries, num) == true)
{
count--;
}
else
{
enteries[count] = num;
}
}
var i;
for(i = 0; i <= enteries.length; i++)
{
document.write(enteries[i]);
document.write("<br>");
}
}
</script>
</head>
<body>
<center><h1>Random Number Generator</h1></center>
<form name="myform" action="" method="GET">Enter the Range of Values
<input type="text" name = "from" value="">to
<input type="text" name = "top" value="">
<p>Enter The Amount of Random Numbers Needed
<input type="text" name = "inputBox" value=""><p>
<input type="button" name="button" value="Generate" onClick=RandomGen(this.form)">
</form>
</body>

You have a syntax error here
<input type="button" name="button" value="Generate" onClick=RandomGen(this.form)">
should be
<input type="button" name="button" value="Generate" onClick="RandomGen(this.form)">
Also this part should be updated, not because it will cause an error but because it is 2011
<script LANGUAGE="JavaScript">
should be
<script type="text/javascript">
Update
Or:
<script>
no need for the type attribute because it is 2018!

You missed a quote:
<input type="button" name="button" value="Generate" onClick="RandomGen(this.form)">

onclick="RandomGen(this.form)"
That part of your code was malformed. onclick is always all lower case and you were missing a "

Your missing a "
<input type="button" name="button" value="Generate" onClick="RandomGen(this.form)">