Develop Reference

Basic math functions in JavaScript to show on HTML page

I would like to make major of basic math functions (addition, subtraction, ect.) to develop in JavaScript. Input parameters should be from HTML webpage, than do the in JavaScript and return result on the same HTML page.
function math() {
//document.getElementById("frm1").innerHTML;
var numb = document.getElementById("number").innerHTML;
var mod = document.getElementById("modifier").innerHTML;
console.log(numb);
console.log(mod);
var sum = 1; //numb + mod; //the 1 is a placeholder
console.log(sum);
sum = document.getElementById("sum").innerHTML;
}
<form id="frm1" action="randScript.js">
Number: <input type="int" name="number" id="number"><br> Modifiers: <input type="int" name="modifier" id="modifier"><br>
<input type="button" onclick="math()" value="Submit">
</form>
<p id="sum"></p>

Your form tag has an action attribute. This means the page will submit your information to the specified page. You can use jQuery to prevent the form from submitting.
$("#yourFormId").on("submit",function(event){event.preventDefault()})
You can also edit the forms action attribute itself to prevent it from submitting.
<form id="frm1" action"javascript:void(0);">

First: The type is text - there is no "int" thing
Number: <input type="text" name="number" id="number">
Second: if we read a bit documentation we figure also out how to get the alue into the JS part
var numb = document.getElementById("number").value;
here you can now do your further homework ;)
Third: Get things back:
either use another input. They work two ways.
document.getElementById("result").value="I did not do my homework alone"
or you place a div somewhere with an id
<div id="result"> </div>
and now you can really use innerHTML in js
document.getElementById("result").innerHTML="I am too lazy";
The rest and to put it all together is now up to you :) Have fun to study :)

Try that if you want to display the sum at the html element:
document.getElementById("sum").innerHTML = sum;
But a more precise Question would help!

There is no int type for form inputs in HTML you can learn here about input types: HTML form input types
<form id="frm1" >
Number1: <input type="number" name="number" id="number1"><br>
Number2: <input type="number" name="number" id="number2"><br>
Modifiers: <input type="text" name="modifier" id="modifier"><br>
<input type="button" onclick="math()" value="Submit">
</form>
<p id = "sum"></p>
<script type="text/javascript">
function math() {
var numb1 = parseInt(document.getElementById("number1").value);
var numb2 = parseInt(document.getElementById("number2").value);
var mod = document.getElementById("modifier").value;
if(mod == '+'){
var sum = numb1 + numb2;
}else if(mod == '-'){
var sum = numb1 - numb2;
}else if(mod == '*'){
var sum = numb1 * numb2;
}
if(sum === undefined){
alert('invalid inputs');
return false;
}else{
document.getElementById("sum").innerHTML = sum;
}
return true;
}

To retrieve inputs values properly use value rather then innerHtml.
Retrieved values are strings so you need to parse them to numbers (with parseInt) before using them in math.
function math() {
const numb = document.getElementById("number").value;
const mod = document.getElementById("modifier").value;
sum = document.getElementById("sum").innerText = parseInt(numb) + parseInt(mod);
}

How to store javascript values into mysql database?

I'm trying to store the users BMI score and comments into mysql database. I'm able to store their height and weight but just not their score and bmi comment.
Any suggestions would be appreciated.
<script type="text/javascript">
function Calculate()
{
//Obtain user inputs
var height=Number(document.getElementById("height").value);
var heightunits=document.getElementById("heightunits").value;
var weight=Number(document.getElementById("weight").value);
var weightunits=document.getElementById("weightunits").value;
//Convert all units to metric
if (heightunits=="inches") height/=39.3700787;
if (weightunits=="lb") weight/=2.20462;
if (heightunits=="cm") height/=100;
//Perform calculation
var BMI=weight/Math.pow(height,2);
//Display result of calculation
document.getElementById("output").innerText=Math.round(BMI*100)/100;
var output = Math.round(BMI*100)/100
if (output<18.5)
document.getElementById("comment").innerText = "Underweight";
else if (output>=18.5 && output<=25)
document.getElementById("comment").innerText = "Normal";
else if (output>=25 && output<=30)
document.getElementById("comment").innerText = "Obese";
else if (output>30)
document.getElementById("comment").innerText = "Overweight";
// document.getElementById("answer").value = output;
}
</script>
</head>
<body>
<div>BMI Calculator</div>
<input type="button" value="Calculate" onclick="Calculate(this.form);">
<input type="submit" name="savebmi" value="SaveBMI">
<p class="font-3">Your BMI is: <span name="output" value="output" type="float" id="output" class="textInput"></span></p>
<p class="font-3">This means you are: <span name="comment" type="text" id="comment"></span> </p>

One thing you could do is change your span tags to input tags and then just change your JavaScript to set the value attribute instead of the innerText. Then when you submit the form, it will pass those values to your PHP script.
You can always style your input boxes to match your paragraph text if don't like the appearance of boxes. For example, start with style='border:none.
JavaScript
//Display result of calculation
document.getElementById("output").value=Math.round(BMI*100)/100;
var output = Math.round(BMI*100)/100
if (output<18.5)
document.getElementById("comment").value = "Underweight";
else if (output>=18.5 && output<=25)
document.getElementById("comment").value = "Normal";
else if (output>=25 && output<=30)
document.getElementById("comment").value = "Obese";
else if (output>30)
document.getElementById("comment").value = "Overweight";
// document.getElementById("answer").value = output;
HTML
<p class="font-3">Your BMI is: <input name="output" type="float" id="output" class="textInput" style="border:none" /></p>
<p class="font-3">This means you are: <input name="comment" type="text" id="comment" style="border:none" /></p>

Elements with id output and comment are not input elements but span, so they are not passed to the PHP script.
You should try to pass this via AJAX to your script, then you can add these values to the request.
Example:
var req = new XMLHttpRequest();
req.onreadystatechange = function() {
if (this.readyState == 4 && this.status == 200) {
// Whatever you want to do with the php response
}
}
req.open("POST", "script.php", true);
req.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
req.send("output=" + output + "&weight=" + weight + ...);
Another workaround is to use hidden input elements, but then you should make a function to validate these or make it non-editable.

Here is a solution to fit your question..
//Display result of calculation
var bmi_result = Math.round(BMI*100)/100;
document.getElementById("output").innerText=bmi_result;
document.getElementById("form_output").innerText=bmi_result;
var comment = '';
if (bmi_result<18.5) {
comment = "Underweight";
} else if (bmi_result>=18.5 && output<=25) {
comment = "Normal";
} else if (bmi_result>=25 && output<=30) {
comment = "Obese";
} else if (bmi_result>30) {
comment = "Overweight";
}
document.getElementById("comment").innerText = comment;
document.getElementById("form_comment").innerText = comment;
In your form:
<input type="hidden" id="form_output" name="output" value="">
<input type="hidden" id="form_comment" name="comment" value="">
<input type="button" value="Calculate" onclick="Calculate(this.form);">

"NaN" result when multiplying more than one value in an array by a number

Note: please pay no attention to my beginnings on the "Decrypt" function, button, etc. It has no relevance towards this question.
I've looked practically everywhere for a fix on here and can't seem to find one due to my kinda strange project. I'm a noob at JavaScript so please tell me anything I could improve on. Here's my project: It's basically a Encrypt/Decrypt message thing based on what key you type in.. When you type in the key, and submit it, it gives the key a value based on it's length and ASCII value:
function submitkey(form) {
keyinp = (form.key.value)
var keyl = keyinp.length
keyasciiout = keyinp.charCodeAt(0)
document.getElementById("asciikeyout").innerHTML =
"<b>" + keyinp + "</b> is your key."
if (keyl > 4) {
keyasciitwo = keyinp.charCodeAt(1)
keyasciithree = keyinp.charCodeAt(2)
keyasciifour = keyinp.charCodeAt(3)
keyasciifive = keyinp.charCodeAt(4)
finalkey = (((keyasciiout + keyasciitwo + keyasciithree + keyasciifour + keyasciifive) / keyl) * 0.5)
}
else { alert("Please choose a new key. It must be 5 or more characters.") }
}
So now you've entered a key and it has a value that plays a role in encrypting/decrypting your messages. Here's the text boxes that you enter in and stuff.
<form name="keyinput">
<input type="text" id="key" name="key">
<br>
<input type="button" name="keysub" id="keysub" value="Submit Key" onclick="submitkey(this.form)">
</form>
<p id="asciikeyout"></p>
<p id="key2"></p>
<br> <br>
<br> <br>
<br> <br>
<form name="field">
<input type="button" name="decryptbutton" onclick="dec(this.form)" value="Decrypt">
<br>
<textarea id="input" rows="4" cols="50" onkeyup="getascii(this.form)" onkeydown="keycheck(this.form)"></textarea>
<br>
<br>
<textarea id="output" rows="20" cols="70" fontsize="18px" readonly></textarea>
</form>
<p id="res2"></p>
By the way, the keycheck() function is just something where if you type in the textbox and don't have anything entered as a key, it will alert you to create a key.
So whenever you type into the input textbox, it runs getascii(this.form), which, btw, just gets the ASCII values of all of the characters you typed and stores them as a variable, in which this case, is "code":
function getascii(form) {
globalinp=(form.input.value)
var str=(form.input.value);
code = new Array(str.length);
for(var i=0;i<str.length;i++){
code[i]=str.charCodeAt(i);
}
encrypt(code)
}
Which, in turn, runs encrypt(), which places the "code" values into an array(i think, this may be the issue. please tell me.):
function encrypt(code) {
sepcode = code.toString().replace(/,/g, " ")
asciiarray = sepcode.split(" ");
arrmult()
}
Which, then again, runs a function called arrmult, which is where the trouble begins (i think).
function arrmult() {
var a = [asciiarray];
var b = a.map((function (x) { return x * finalkey; }).bind(this));
document.getElementById("output").innerHTML =
b
}
The above code I got from this website. What it does is takes each individual value of the array assigned as the variable A, in this case all of the ASCII values of whatever you typed in the box, and multiplies them by a certain value, which I have set as the value of the key. Note: When I replace the variable A with a string of numbers, like this:
var a = [127,93,28];
It seems to be working perfectly fine. But, when I use asciiarray instead, it returns back with a value of "NaN", but only when I do more than ONE character. When I only type one character and have the variable a set as this:
var a = [asciiarray];
It works perfectly fine. But when it updates, and has two or more characters, it results as "NaN" even though the value of asciiarray is the exact same as the numbers above. And when you do reply, please help me realize where to replace what I've done wrong, as I'm a JavaScript complete noob.
If you wish to look at the code completely, here it is. You can even copy and paste it into an HTML file if you wish:
<html>
<body>
<head>
<title>Ascii Encryption</title>
</head>
<script>
var code="test"
var sepcode="test"
var keyinp="test"
var keyasciiout="test"
var finalkey="test"
var globalinp="test"
var globalascarr="test"
var multex="test"
var keyasciitwo="test"
function getascii(form) {
globalinp=(form.input.value)
var str=(form.input.value);
code = new Array(str.length);
for(var i=0;i<str.length;i++){
code[i]=str.charCodeAt(i);
}
encrypt(code)
}
</script>
<script>
function submitkey(form) {
keyinp = (form.key.value)
var keyl = keyinp.length
keyasciiout = keyinp.charCodeAt(0)
document.getElementById("asciikeyout").innerHTML =
"<b>" + keyinp + "</b> is your key."
if (keyl > 4) {
keyasciitwo = keyinp.charCodeAt(1)
keyasciithree = keyinp.charCodeAt(2)
keyasciifour = keyinp.charCodeAt(3)
keyasciifive = keyinp.charCodeAt(4)
finalkey = (((keyasciiout + keyasciitwo + keyasciithree + keyasciifour + keyasciifive) / keyl) * 0.5)
}
else { alert("Please choose a new key. It must be 5 or more characters.") }
}
</script>
<script>
function encrypt(code) {
sepcode = code.toString().replace(/,/g, " ")
asciiarray = sepcode.split(" ");
arrmult()
}
</script>
<script>
function arrmult(none) {
var a = [asciiarray];
var b = a.map((function (x) { return x * finalkey; }).bind(this));
document.getElementById("output").innerHTML =
b
}
</script>
<script>
function dec(form) {
var input = (form.input.value)
var inputdiv = (input / finalkey)
var decrypted = String.fromCharCode(inputdiv)
alert(decrypted)
}
</script>
<script>
function keycheck(form) {
if (finalkey != null) {
null
} else {
alert("Please enter a key. This will determine how your encryptions and decryptions are made.")
}
}
</script>
<center>
<br> <br>
<br> <br>
<form name="keyinput">
<input type="text" id="key" name="key">
<br>
<input type="button" name="keysub" id="keysub" value="Submit Key" onclick="submitkey(this.form)">
</form>
<p id="asciikeyout"></p>
<p id="key2"></p>
<br> <br>
<br> <br>
<br> <br>
<form name="field">
<input type="button" name="decryptbutton" onclick="dec(this.form)" value="Decrypt">
<br>
<textarea id="input" rows="4" cols="50" onkeyup="getascii(this.form)" onkeydown="keycheck(this.form)"></textarea>
<br>
<br>
<textarea id="output" rows="20" cols="70" fontsize="18px" readonly></textarea>
</form>
<p id="res2"></p>
</center>
</body>
</html>

radio button .checked to perform a math expression using user input javascript

I have two textboxes where a user enters a number into each one and then clicks a radio button to select the mathematical operation to be performed upon the calculate button.This is for a homework assignment, so only javascript and html
are being used, no jquery. Currently when I click the button, nothing appears to happen and I am getting no console errors...
HTML
<div>
<p>Enter two numbers, select a math, then click the button.<br>
The answer will be shown below.</p>
<form>
1st number: <input type="text" name="number1">
2nd number: <input type="text" name="number2">
<br>
<input type="radio" name="add">Add <br>
<input type="radio" name="subtract">Subtract <br>
<input type="radio" name="multiply">Multiply <br>
<input type="radio" name="division">Division <br>
<input type="button" name="calc" onclick="calculate()" value="Calculate"> <br>
</form>
<p id="math_res"></p>
</div>
Javascript
function calculate(){
var num1 = parseInt("document.getElementsByName('number1').value;", 10);
var num2 = parseInt("document.getElementsByName('number2').value;", 10);
var add = document.getElementsByName("add");
var sub = document.getElementsByName("subtract");
var multi = document.getElementsByName("multiply");
var divis = document.getElementsByName("division");
var res = document.getElementById("math_res").innerHTML;
if (add.checked == true){
res = num1 + num2;
}
else if ( sub.checked == true){
res = num1 + num2;
}
else if (multi.checked == true){
res = num1 * num2;
}
else if (divis.checked == true){
res = num1 / num2;
}
}
I thought my function would take the input from the two text boxes and convert the user input to an integer and assign them to variable num1 and num2. Then assign each radio button to a variable to reduce typing of document.get...
that each if statement would check to see if that radio but was checked. If true perform calculation if false move to next if statement and display the results in a paragraph element.
where did I go wrong?

You have a couple of issues.
getElementsByName returns a collection of elements, not a single element so:
var add = document.getElementsByName("add");
will assign undefined to add. But you don't need to use it, just reference the controls as named properties of the form. Pass a reference to the button from the listener:
<input type="button" name="calc" onclick="calculate(this)" value="Calculate">
Then in the function get the form:
function calculate(element) {
var form = element.form;
Now just do:
var num1 = parseInt(form.number1.value, 10);
and so on, which also fixes the other issues you have with referencing the controls.
Also, radio buttons need to have the same name so that only one is selectable, so as Felix says, give them all the same name and differentiate on value (or class or some other attribute value). You'll need to loop over them to find out the operation to perform, so the HTML might be:
<input type="radio" name="operation" value="add">Add <br>
<input type="radio" name="operation" value="subtract">Subtract <br>
<input type="radio" name="operation" value="multiply">Multiply <br>
<input type="radio" name="operation" value="division">Division <br>
Then to get the operation:
var radios = form.operation;
var op;
for (var i=0; i<radios.length; i++) {
if (radios[i].checked) {
op = radios[i].value;
break;
}
}
Now check the value of op to work out whether to add, subtract, etc.
Here's a quick example, I don't recommend inline scripts like this but it's handy for playing.
<form>
<input type="radio" name="operation" value="add">Add <br>
<input type="radio" name="operation" value="subtract">Subtract <br>
<input type="radio" name="operation" value="multiply">Multiply <br>
<input type="radio" name="operation" value="division">Division <br>
<input type="button" onclick="
var form = this.form;
var radios = form.operation;
var op;
for (var i=0; i<radios.length; i++) {
if (radios[i].checked) {
op = radios[i].value;
break;
}
}
form.selectedOperation.value = op || 'No operation selected';
" value="Get selected operation">
<input type="text" readonly name="selectedOperation"><br>
<input type="reset">
</form>

There are a few issues I can notice.
1.
getElementsByName returns a NodeList, which is Array-like. You need to retrieve the first element in the NodeList before accessing its value. For example,
document.getElementsByName('number1')[0].value
2.
You are passing a literal code string to parseInt. You should write something like
parseInt(document.getElementsByName('number1')[0].value, 10);
3.
The code var res = document.getElementById('math_res').innerHTML stores a reference to the innerHTML of the element. When you assign res = num1 + num2 for example, you are simply overwriting the reference, instead of actually altering the innerHTML. To correct this,
var elem = document.getElementById('math_res');
// later...
elem.innerHTML = num1 + num2;
4. You are incorrectly defining multiple radio buttons with different names. In order for the browser to render them as a "radio button group" where only one can be selected, they must have the same name, but different "value" attributes. See RobG's answer or the Plunkr below for an example of how to define the radio button group and extract its value using JavaScript.
A working version of your code is here.
Edit Please note that these are minimal edits to make your code work. RobG's answer shows a more correct way of extracting the values of form fields.

Here is my version, hope it helps you.
<!DOCTYPE html>
<html>
<body>
<div>
<p>Enter two numbers, select a math, then click the button.<br>
The answer will be shown below.</p>
<form>
1st number: <input type="text" name="number1" id = 'number1'>
2nd number: <input type="text" name="number2" id = 'number2'>
<br>
<input type="radio" name="button" id = 'add' >Add <br>
<input type="radio" name="button" id = 'substract'>Subtract <br>
<input type="radio" name="button" id = 'multiply'>Multiply <br>
<input type="radio" name="button" id = 'division'>Division <br>
<input type="button" name="calc" onclick="calculate()" value="Calculate"> <br>
</form>
<p id="math_res"></p>
</div>
<script>
function calculate(){
//Obtaining the references to the text inputs
var number1 = parseInt(document.getElementById('number1').value);
var number2 = parseInt(document.getElementById('number2').value);
//Reference of the result Box
var resultBox = document.getElementById('math_res');
resultBox.innerHTML = '';
//Reference of the radio buttons
var buttonAdd = document.getElementById('add');
var buttonSubstract = document.getElementById('substract');
var buttonMultiply = document.getElementById('multiply');
var buttonDivision = document.getElementById('division');
//Make the magic
if(buttonAdd.checked == true){
resultBox.innerHTML = number1 + number2
}
else{
if(buttonSubstract.checked == true){
resultBox.innerHTML = number1 - number2
}
else{
if(buttonMultiply.checked == true){
resultBox.innerHTML = number1 * number2
}
else{
if(buttonDivision.checked == true){
resultBox.innerHTML = number1 / number2
}
}
}
}
}
</script>
</body>

Grab form fields and calculate based on inputs

I'm getting an undefined error and don't know why this isn't working.
It's supposed to divide the rent by the amount of roommates:
function splitRent() {
var roommates = document.getElementById("rent");
var rent = document.getElementById("rent");
var rentEach = rent / roommates;
if (document.getElementById("submit") == true) {
document.write("You each should pay" + " " + rentEach)
} else {
document.alert("Gimme info")
}
};
<h1>Roommate Room Splitter</h1>
<form id="myForm">
Roommates:
<input type="text" name="roommates" id="roommates">
<br/>Rent:
<input type="text" name="rent" id="rent">
<br/>
<input type='submit' id='submit' value='Submit' onclick="splitRent()" />
</form>

You want to take the value of the fields, not the fields themselves.
document.getElementById() returns the node, but you want the value of the input field:
var rent = document.getElementById("rent").value;
Also, you're getting the value of the rent twice; you want to check the roommates as well.
var roommates = document.getElementById("roommates").value;
Lastly, document.getElementById("submit") == true doesn't mean anything: you're comparing a button node with a boolean value, which doesn't make sense. If you want to check to make sure that both fields are filled, try this:
if(roommates && rent){
//do calculations
}else{
window.alert("Enter something"); //note that it's window.alert(), not document.alert(), which is not a function
As it stands, this allows people to enter things that are not numbers; there are two things that you could do to fix that.
Use parseInt()/parseFloat() to ensure that you're extracting a number
Check that you actually have a number before doing calculations
You'd do something like this:
var rent = parseInt(document.getElementById("rent").value);
var roommates = parseFloat(document.getElementById("rooommates").value);
If you use the checking I've done above (rent && roommates), the validation will take place there (it checks for both empty and NaN values).
function splitRent() {
var roommates = parseInt(document.getElementById("roommates").value);
var rent = parseFloat(document.getElementById("rent").value);
var rentEach = rent / roommates;
if (roommates && rent) {
document.write("You each should pay" + " " + rentEach)
} else {
window.alert("Gimme info")
}
};
<h1>Roommate Room Splitter</h1>
<form id="myForm">
Roommates:
<input type="text" name="roommates" id="roommates">
<br/>Rent:
<input type="text" name="rent" id="rent">
<br/>
<input type='submit' id='submit' value='Submit' onclick="splitRent()" />
</form>

Shouldn't this be:
var roommates = document.getElementById("roommates").value;
var rent = document.getElementById("rent").value;
Do you always get "1" for your result?