Develop Reference

Converting a value using JavaScript

Somehow my below JavaScript code to convert the value from kilometers to nautical mile doesn't seem to work. It seems very simple but I could not find out why I am. I would appreciate your help.
<div class="calculator">
<form>
Enter a value in Kilometers:
<input type="text" id="kM" value="1000"> Result in Nautical Mile:
<input type="text" id="nM" value="" disabled>
<button onclick="return calculate();" id="calculate">CALCULATE</button>
</form>
</div>
<script>
function convert(kiloMeter) {
return kiloMeter / 1.852;
}
function calculate() {
var kMeter = Number(document.getElementById("kM").value);
var convertedValue = convert(kMeter);
document.getElementById("nM").innerHTML =
convertedValue;
return false;
}
</script>

There are at least two issues causing your script to not work
Input elements don't have an innerHMTL property. They have a value. So document.getElementById("nM").innerHTML should be document.getElementById("nM").value
At that point everything should be fine. You shouldn't need to change your button type to button since you return false from the function and the button returns false to the form, stopping the form from submitting. HOWEVER there appears to be an issue with naming your function calculate (at least in Chrome and Firefox) the same as the id of the element (id="calculate"). Changing the name of the function or the id fixes the issue.
function convert(kiloMeter) {
return kiloMeter / 1.852;
}
function calculate() {
var kMeter = Number(document.getElementById("kM").value);
var convertedValue = convert(kMeter);
document.getElementById("nM").value = convertedValue;
return false;
}
<div class="calculator">
<form>
Enter a value in Kilometers:
<input type="text" id="kM" value="1000"> Result in Nautical Mile:
<input type="text" id="nM" value="" disabled>
<button onclick="return calculate();" id="xcalculate">CALCULATE</button>
</form>
</div>

For input tag you should use value rather than innerHtml. You do not need to return false also.
<div class="calculator">
<form>
Enter a value in Kilometers:
<input type="text" id="kM" value="1000"> Result in Nautical Mile:
<input type="text" id="nM" value="" disabled>
<button type='button' onclick="calculate()" id="">CALCULATE</button>
</form>
</div>
<script>
function convert(kiloMeter) {
return kiloMeter / 1.852;
}
function calculate() {
var kMeter = Number(document.getElementById("kM").value);
var convertedValue = convert(kMeter);
document.getElementById("nM").value =
convertedValue;
}
</script>

You should use value instead of innerHTML:
document.getElementById("nM").value = convertedValue;

JavaScript - Trying to add value to text field by clicking button

Cant get my function to work and add the value of the button to the text field when clicked by user.
HTML
<form name="testing" action="test.php" method="get">Chords:
<textarea name="field"></textarea>
<input type="button" value="G" onClick="addToField('G');">
<input type="button" value="C" onClick="addToField('C');">
<input type="button" value="Am" onClick="addToField('Am');">
<input type="button" value="F" onClick="addToField('F');">
JavaScript
<script language="javascript" type="text/javascript">
function addToField(crd){
document.testing.field.value += crd;
}
</script>
Really stuck trying to understand whats wrong here.
Hope this shows what I am trying to achieve: https://jsfiddle.net/034hyjo2/6/

You're accessing the object incorrectly
<script language="javascript" type="text/javascript">
function addToField(crd){
document.getElementByName("testing").value += crd;
}
</script>
Or, give the element an ID and use getElementByID("testing").value.
I usually find that works better anyway...

If you're just getting it in the fiddle, it works by putting the script tag above your HTML:
<script>
var addToField = function(c) {
document.testing.field.value += c;
};
</script>
<form name="testing" action="test.php" method="get">Chords:
<textarea name="field"> </textarea>
<input type="button" value="G" onClick="addToField('G');">
<input type="button" value="C" onClick="addToField('C');">
<input type="button" value="Am" onClick="addToField('Am');">
<input type="button" value="F" onClick="addToField('F');">
</form>

Your JSFiddle is way wrong. You're question here is better. You want to be using document.getElementById('field').value += crd; instead of document.testing.field.value += crd;
try this:
<form name="testing" action="test.php" method="get">Chords:
<textarea id="field" name="field"> </textarea> ---note the addition of the ID parameter
<input type="button" value="G" onClick="AddToField('G');">
<input type="button" value="C" onClick="AddToField('C');">
<input type="button" value="Am" onClick="AddToField('Am');">
<input type="button" value="F" onClick="AddToField('F');">
</form>
<script>
function AddToField(c) {
document.getElementById('field').value += c;
};
</script>
Also functions shouldn't be camelCase but Pascal case ;)

Using javascript functions in HTML

I am creating a small webpage that will add two input fields together and place the result in another input field. This is what I have:
<html>
<head>
<title>Calculator</title>
<script type="text/javascript">
function add(){
var num1 = parseInt(document.calc.num1.value);
var num2 = parseInt(document.calc.num2.value);
var answer = (num1+num2);
document.getElementById('res').value = answer;
}
</script>
</HEAD>
<BODY>
<FORM NAME="calc">
<INPUT TYPE ="button" NAME="add" Value="+" onClick="add()">
<hr/>
<INPUT TYPE ="text" NAME="num1" Value="">
<INPUT TYPE ="text" NAME="num2" Value="">
<hr/>
<INPUT TYPE ="text" ID="res" NAME="result" VALUE="">
</FORM>
</BODY>
</HTML>
And I am getting the following error when I press the + button.
Uncaught TypeError: object is not a function

Try changing the function name from add to addNumbers or something like that.

onclick is the right attribute to handle click

onClick="add()"
Switch this bit to
onclick="add()"

The problem is the name of the function "add()", change the name and you will see that it will works!

HTML
<p>
<label for="field1">Field 1</label>
<input type="number" id="field1"/>
</p>
<p>
<label for="field2">Field 2</label>
<input type="number" id="field2"/>
</p>
<p>
<label for="total">Total</label>
<input readonly type="number" id="total"/>
</p>
<p>
<input type="button" id="calc" value="Calculate"/>
</p>
Javascript
Goes in a script tag in head.
function sumFields(fields) {
var total = 0;
// goes through each field and adds them to the total
for(var i=0,l=fields.length; i<l; i++)
{ total += parseInt(document.getElementById(fields[i]).value); }
document.getElementById('total').value = total;
}
function calc_click() {
// runs when the button is clicked
sumFields(['field1','field2']);
}
// main function
function init() {
// add button functionality
document.getElementById('calc').addEventListener('click',calc_click,false);
}
// fires when the DOM is loaded
document.addEventListener('DOMContentLoaded',init,false);

js wont show result of calculation

Quick newbie question, i'm sure it is simple to you, but i cant get my head around to figure out why my code wont work. Checked online, seems that i'm doing everything fine, but still wont work... All i'm trying to do, is to make simple calc and display that in diff field. I have tryed external and internal JS.
Here's my code:
<script type="text/javascript">
function calculate(){
var a = document.calculate.first.value;
var b = document.calculate.second.value;
var c = parseInt(a) + parseInt(b);
document.calculate.result.value = c;
}
</script>
<body>
<form name="calculate">
<input type="text" name="first" size="5">
<input type="text" name="second" size="5">
<input type="button" onclick="calculate()">
<input type="text" name="result" id="result" size="5">
</form>
</body>

Chrome says:
Uncaught TypeError: object is not a function (onclick)
Give a different name to the form and the onclick handler! Here is a test.

Here is the corrected code :
<html>
<head>
<script type="text/javascript">
function calculate(){
var a = document.getElementById('first').value;
var b = document.getElementById('second').value;
var c = parseInt(a) + parseInt(b);
document.getElementById('result').value = c;
}
</script>
</head>
<body>
<form name="calculateform">
<input type="text" id="first" size="5">
<input type="text" id="second" size="5">
<input type="button" onclick="calculate()">
<input type="text" id="result" id="result" size="5">
</form>
</body>
</html>

Its probably because you are using the same name for the form as for your js function.
Working example:
<html>
<head>
<script type="text/javascript">
function calculate(){
alert(document.calculatex.first.value);
var a = document.calculatex.first.value;
var b = document.calculatex.first.value;
var c = parseInt(a) + parseInt(b);
document.calculatex.result.value= c;
}
</script>
</head>
<body>
<form name="calculatex">
<input type="text" name="first" size="5"/>
<input type="text" name="second" size="5"/>
<input type="button" value="calculate" onclick="calculate();"/>
<input type="text" name="result" id="result" size="5"/>
</form>
</body>
Have a look into JQuery library (convenient for getting/setting field values).

HTML display result in text (input) field?

I have a simple HTML form, with 3 input field, when you hit = button, it suppose to add 2 numbers that you typed in the first 2 input fields and display result in 3rd filed. Is it possible to do that? (I need result in a box (or table) or some thing rather than in plain text). I try the following but doesn't work (it does nothing), can somebody help me?
<HTML>
<HEAD>
<TITLE>Sum</TITLE>
<script type="text/javascript">
function sum()
{
var num1 = document.myform.number1.value;
var num2 = document.myform.number2.value;
var sum = parseInt(num1) + parseInt(num2);
document.getElementById('add').innerHTML = sum;
}
</script>
</HEAD>
<BODY>
<FORM NAME="myform">
<INPUT TYPE="text" NAME="number1" VALUE=""> +
<INPUT TYPE="text" NAME="number2" VALUE="">
<INPUT TYPE="button" NAME="button" Value="=" onClick="sum()">
<INPUT TYPE="text" ID="add" NAME="result" VALUE="">
</FORM>
</BODY>
</HTML>

innerHTML sets the text (including html elements) inside an element. Normally we use it for elements like div, span etc to insert other html elements inside it.
For your case you want to set the value of an input element. So you should use the value attribute.
Change innerHTML to value
document.getElementById('add').value = sum;

<HTML>
<HEAD>
<TITLE>Sum</TITLE>
<script type="text/javascript">
function sum()
{
var num1 = document.myform.number1.value;
var num2 = document.myform.number2.value;
var sum = parseInt(num1) + parseInt(num2);
document.getElementById('add').value = sum;
}
</script>
</HEAD>
<BODY>
<FORM NAME="myform">
<INPUT TYPE="text" NAME="number1" VALUE=""/> +
<INPUT TYPE="text" NAME="number2" VALUE=""/>
<INPUT TYPE="button" NAME="button" Value="=" onClick="sum()"/>
<INPUT TYPE="text" ID="add" NAME="result" VALUE=""/>
</FORM>
</BODY>
</HTML>
This should work properly.
1. use .value instead of "innerHTML" when setting the 3rd field (input field)
2. Close the input tags

Do you really want the result to come up in an input box? If not, consider a table with borders set to other than transparent and use
document.getElementById('sum').innerHTML = sum;

With .value and INPUT tag
<HTML>
<HEAD>
<TITLE>Sum</TITLE>
<script type="text/javascript">
function sum()
{
var num1 = document.myform.number1.value;
var num2 = document.myform.number2.value;
var sum = parseInt(num1) + parseInt(num2);
document.getElementById('add').value = sum;
}
</script>
</HEAD>
<BODY>
<FORM NAME="myform">
<INPUT TYPE="text" NAME="number1" VALUE=""/> +
<INPUT TYPE="text" NAME="number2" VALUE=""/>
<INPUT TYPE="button" NAME="button" Value="=" onClick="sum()"/>
<INPUT TYPE="text" ID="add" NAME="result" VALUE=""/>
</FORM>
</BODY>
</HTML>
with innerHTML and DIV
<HTML>
<HEAD>
<TITLE>Sum</TITLE>
<script type="text/javascript">
function sum()
{
var num1 = document.myform.number1.value;
var num2 = document.myform.number2.value;
var sum = parseInt(num1) + parseInt(num2);
document.getElementById('add').innerHTML = sum;
}
</script>
</HEAD>
<BODY>
<FORM NAME="myform">
<INPUT TYPE="text" NAME="number1" VALUE=""/> +
<INPUT TYPE="text" NAME="number2" VALUE=""/>
<INPUT TYPE="button" NAME="button" Value="=" onClick="sum()"/>
<DIV ID="add"></DIV>
</FORM>
</BODY>
</HTML>