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Outputs not showing in simple odd/even code

I've just started beginning to code in JavaScript (my first attempt at any so please be patient!), so have just set myself a simple project just to create a input box, and was hoping upon clicking the calculate button to generate a "Even" or "Odd" output that shows up below the box. But somehow I can't get anything to show up. Any ideas what I'm doing wrong?
function myFunction() {
// define var num
var num = document.getElementById("number").value;
//use of if function as number is odd or even (modulo = 0 or 1)
if (num % 2 === 0) {
document.writeIn("Even");
} else {
document.writeIn("Odd");
}
}
<table id="number">
Number: <input type="number" name="name">
<input type="button" onclick="myFunction()" value="Calculate"></table>

You need to take an input with type 'text' and an id of 'number'.
Then get this value of the input and assign to another element the result, because document.writeln does not work after the page is rendered by the user agent.
function myFunction() {
var num = document.getElementById("number").value;
document.getElementById("type").innerHTML = num % 2 ? "Odd": "Even";
}
Number: <input type="text" id="number">
<input type="button" onclick="myFunction()" value="Calculate">
<div id="type"></div>

How to print random string from a selection of user form inputs javascript/jquery

var textEntered = function() {
var input = document.userNameForm.userInput.value;
if(input) {
document.getElementById("resultText").innerHTML += input + "<br>";
}
}
This is what I have so far and this obviously just prints out the user inputs onto the screen in a list. But I want to somehow store all these user inputs from the form I have in my HTML, (maybe in an array?) and maybe assign each to a number and use Math.floor(Math.random()) to print out a random result. (I'm just making a little/random site where you put in the names of your friends and it returns and prints a random name from the names that you give it, if that makes sense).
I'm a beginner just so you know

function textEntered() {
var inputs = [];
$('form input').each((i,e)=>inputs.push(e.value));
if (inputs) {
document.getElementById("resultText").innerHTML += inputs[Math.floor(Math.random()*inputs.length)] + "<br>";
}
}
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<form>
<input value="Hello">
<input value="World">
<input value="from Stardust">
<button onclick="textEntered()">Submit Now!</button>
</form>
<div id="resultText">Submit it!
<br><br>
</div>
Is this essentially what you are looking for?

how to get the current values of an input on button click event

I have a bunch of div's that have the same functionality and I'm trying to write a function for them.
Basically they have a predetermined value and a user input value and those need to be multiplied.
I've looked through a bunch of other questions and this is the closest one I could find. Almost exactly, but none of those answers work.
Any help would be great. Thanks in advance!
<div>
<label>enter value for multiple here</label>
<input type="text" class="multiple" factor="foo1"/>
<button type="button" class="multiplyBtn">Click here to multiply these numbers</button>
<label>enter value for multiple here</label>
<input type="text" class="multiple" factor="foo2"/>
<button type="button" class="multiplyBtn">Click here to multiply these numbers</button>
</div>
Here's the JS:
$('.mulitplyBtn').click(function() {
var factor = $(this).closest('attr.factor').val();
var multiple = $(this)closest('.multiple').val();
answer = (factor * multiple);
};

This would work:
$('.multiplyBtn').click(function() { // you had multiplyBtn spelled wrong here
var cur = $('.multiplyBtn').index($(this)); // get index of clicked btn
var factor = $('.multiple').eq(cur).data('factor'); // get factor from matching input
var multiple = $('.multiple').eq(cur).val(); // get value from matching input
answer = (Number(factor) * Number(multiple)); // make sure both are numbers then multiply
alert(answer);
});
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<div>
<label>enter value for multiple here</label>
<input type="text" class="multiple" data-factor="4" />
<button type="button" class="multiplyBtn">Click here to multiply these numbers</button>
<br>
<label>enter value for multiple here</label>
<input type="text" class="multiple" data-factor="7" />
<button type="button" class="multiplyBtn">Click here to multiply these numbers</button>
</div>

In the first line you used " and ' try using the same quotes (I mean using ".multiplyBtn" or '.multiplyBtn' )
Second time, 3rd line you didn't use any quote when calling .multiple. So turn it in that format : var multiple = $(this)closest('.multiple').val()
let me know the result

You have at least two typos and are using the wrong jQuery function.
Typos:
$('.mulitplyBtn') should be $('.mulitplyBtn')
$(this)closest should be $(this).closest
Wrong function:
closest() searches the parents, and the only parent here is the DIV with no class. What you probably want is to use parent() to go up to the DIV, then find() to search the parent's children for a specific element:
$(this).parent().find('.multiple').val()

attr.factor does not work like this.
try it like this:
$('.multiplyBtn').click(function() {
var container = $(this).prev('.multiple'); //don't forget the "dot"
var multiple = container.val();
var factor = container.attr('factor'); //since it is the same container.
var answer = (factor * multiple); //what exactly are you tryin to multiply?
};

JAVASCRIPT: Getting values inside an array

I'm having a problem in calling the values I entered in the numberbox (I don't know what should I call it... if there's a textbox, there should be a numberbox. lol). If I enter "123456", the value of sum should be "21", but what happens is that the value of sum is "0123456".
<input type="number" name="user" id="input" maxlength="6" size="6" required>
<input type="button" onClick="Calculate()" value="Calculate">
<script type="text/javascript">
function Calculate(){
var user = [];
user=document.getElementById("input").value;
if(user.length==6){
var sum=0;
for (i=0;i<user.length;i++){
sum=sum+user[i];
}
var ave=sum/6;
window.alert("Sum is: "+sum);
window.alert("Average is: "+ave);
}
else
window.alert("Please input EXACTLY 6 numbers.");
}
</script>

You are retrieving a string breaking it into parts and adding it back together.You need to convert the string into an integer first. To find out the multiple ways to do this, a very good answer on that is written here:
How do I convert a string into an integer in JavaScript?
sum = sum + parseInt(user[i],10);
Should work

result of input box times 2 appears in window not div

I'm trying to get a text box where you can enter a number and then you click the button and it will multiply it by two and display that result in theDiv. Right now, it opens a new page for the result, and displays the entered number, not the number times two. What am I doing wrong? Beginner here, please be gentle! Thank you!!
<html>
<script>
function doubleit()
{
var theNumber=document.write(parseFloat(document.getElementById('theInput').value));
var doubleNumber =document.getElementById('theNumber')*2;
document.getElementById('theDiv').innerHTML(document.getElementById('doubleNumber'))
}
</script>
<body>
<p>Value: <input type="text" id="theInput" value="" size=10>
<input type="button" id="theButton" value="click me!" onclick="doubleit()"></p>
<div id="theDiv"></div>
</body>
</html>

It's the call to document.write that is replacing the page. Remove it:
var theNumber=parseFloat(document.getElementById('theInput').value);
When you want the value of a variable, you shouldn't use document.getElementById:
var doubleNumber = theNumber * 2;
innerHTML is a property, not a method:
document.getElementById('theDiv').innerHTML = doubleNumber;

var doubleNumber = Number(theNumber, 10)*2;
document.getElementById('theDiv').innerHTML(doubleNumber);

Something like this
function doubleit()
{
var theNumber=parseFloat(document.getElementById('theInput').value) * 2;
document.getElementById('theDiv').innerHTML = theNumber;
}

Try This Solution :
Use the id of your button to call the function to calculate result.
theButton.onclick = function doubleit()
{
//Simply get the number from user and parse it as float.
var theNumber=parseFloat(document.getElementById('theInput').value);
//Multiply it with 2
var doubleNumber =theNumber*2;
//Display the result in another div
document.getElementById('theDiv').innerHTML = doubleNumber;
}
Demo