Kevin Powell - Community•2w ago

How to display value or data in HTML with Javascript

I'm currently struggling with displaying values in HTML. I'm recreating the tip calculator as seen in the image linked below, i've marked the parts to show which labels/inputs im talking about. For now im not using the tip buttons since im mostly focussed on learning how to use the DOM and displaying/working with values that way. This also means the totalAmount is empty since its the same as the bill as there are no tips calculated. 1 The input label called "Bill" 2 The input label called "amountOfPeople" 3 the div was which has <div> 0, 00 </div> in it, which is called "totalPerPerson" 4 the div was which has <div> 0, 00 </div> in it, which is called "totalAmount" Planning/Flowcharting 1 Put a value in the input label bill 2 obtain/store this value 3 Put a value in the input label amountOfPeople 4 obtain/store this value 5 calculate the formula by adding bill + amountOfPeople 6 store the result of the formula 7 display the formula in the totalPerPerson div, replacing the 0,00 8 display the formula in the totalAmount div, replacing the 0,00 Code

// Input labels
const bill = document.getElementById("bill").value
const amountOfPeople = document.getElementById("amountOfPeople").value
// Result divs 
const totalPerPerson = document.getElementById("totalPerPerson")
const totalAmount = document.getElementById("totalAmount")
// Formula
let billPerPerson = bill / amountOfPeople;

// Display in div
totalPerPerson.textContent = billPerPerson

// Input labels
const bill = document.getElementById("bill").value
const amountOfPeople = document.getElementById("amountOfPeople").value
// Result divs 
const totalPerPerson = document.getElementById("totalPerPerson")
const totalAmount = document.getElementById("totalAmount")
// Formula
let billPerPerson = bill / amountOfPeople;

// Display in div
totalPerPerson.textContent = billPerPerson

My question is, how can i make it work in the way that if i type the price and amount in both input fields, it automatically shows up in the div without having to use buttons to submit or statically display the value. it not about making the calculator work but more so about the syntax/ways to display or work with the data

25 Replies

Jochem•2w ago

you can tie a input event to the inputs, then run the same code that would update the fields as when you press the button (so that's elem.addEventListener('input', () => {});) (updated the messages, keypress is apparently deprecated) it fires every time an input/select/textarea changes through direct user interaction

rayannn•2w ago

so that would be like this? does that mean id have to do it twice, once for bill and one for amountOfPeople?

// add the Event listener
bill.addEventListener('input', () => {
totalPerPerson.textContent = billPerPerson
};)

// add the Event listener
amountOfPeople.addEventListener('input', () => {
totalPerPerson.textContent = billPerPerson
};)

// add the Event listener
bill.addEventListener('input', () => {
totalPerPerson.textContent = billPerPerson
};)

// add the Event listener
amountOfPeople.addEventListener('input', () => {
totalPerPerson.textContent = billPerPerson
};)

Jochem•2w ago

assuming billPerPerson is a global variable with the value you want, yeah. Though you can consolidate that:

function updateTotal() {
  totalPerPerson.textContent = billPerPerson;
}
bill.addEventListener('input', updateTotal);
amountOfPeople.addEventListener('input', updateTotal);

function updateTotal() {
  totalPerPerson.textContent = billPerPerson;
}
bill.addEventListener('input', updateTotal);
amountOfPeople.addEventListener('input', updateTotal);

or alternatively stick the listener on the parent, that should work too:

billParentForm.addEventListener('input', updateTotal);

billParentForm.addEventListener('input', updateTotal);

rayannn•2w ago

Looking at your code and wondered something, is my initial code good enough structure wise or am i missing out on things? aside from your solution

// Input labels
const bill = document.getElementById("bill").value
const amountOfPeople = document.getElementById("amountOfPeople").value
// Result divs 
const totalPerPerson = document.getElementById("totalPerPerson")
const totalAmount = document.getElementById("totalAmount")
// Formula
let billPerPerson = bill / amountOfPeople;

// Display in div
totalPerPerson.textContent = billPerPerson

// your solution

// Input labels
const bill = document.getElementById("bill").value
const amountOfPeople = document.getElementById("amountOfPeople").value
// Result divs 
const totalPerPerson = document.getElementById("totalPerPerson")
const totalAmount = document.getElementById("totalAmount")
// Formula
let billPerPerson = bill / amountOfPeople;

// Display in div
totalPerPerson.textContent = billPerPerson

// your solution

Jochem•2w ago

hmm, the main thing I'd notice now is that let billPerPerson = bill / amountOfPeople; will run only once, so it won't update unless you update it yourself so like this

function updateTotal() {
  billPerPerson = bill / amountOfPeople
  totalPerPerson.textContent = billPerPerson;
}

function updateTotal() {
  billPerPerson = bill / amountOfPeople
  totalPerPerson.textContent = billPerPerson;
}

rayannn•2w ago

ya thats a hunch i had, i wasnt sure how to create formula's and use them multiple times

Jochem•2w ago

actually, gimme a sec, I'll rewrite some stuff with some comments

// Inputs
// removed the value, the value of bill won't update dynamically, so you need a reference to the field instead
const bill = document.getElementById("bill");
const amountOfPeople = document.getElementById("amountOfPeople");
// Result divs 
const totalPerPerson = document.getElementById("totalPerPerson");
const totalAmount = document.getElementById("totalAmount");

// Formula
//moved the value references here
let billPerPerson = bill.valueAsNumber / amountOfPeople.valueAsNumber; //valueAsNumber returns a number instead of a string.

// Display in div
totalPerPerson.textContent = billPerPerson

// your solution
function updateTotal() {
  //recalculate the bill
  billPerPerson = bill.valueAsNumber / amountOfPeople.valueAsNumber; //have to keep recalculating, and re-fetching the values
  totalPerPerson.textContent = billPerPerson;
}
bill.addEventListener('input', updateTotal);
totalPerPerson.addEventListener('input', updateTotal);

// Inputs
// removed the value, the value of bill won't update dynamically, so you need a reference to the field instead
const bill = document.getElementById("bill");
const amountOfPeople = document.getElementById("amountOfPeople");
// Result divs 
const totalPerPerson = document.getElementById("totalPerPerson");
const totalAmount = document.getElementById("totalAmount");

// Formula
//moved the value references here
let billPerPerson = bill.valueAsNumber / amountOfPeople.valueAsNumber; //valueAsNumber returns a number instead of a string.

// Display in div
totalPerPerson.textContent = billPerPerson

// your solution
function updateTotal() {
  //recalculate the bill
  billPerPerson = bill.valueAsNumber / amountOfPeople.valueAsNumber; //have to keep recalculating, and re-fetching the values
  totalPerPerson.textContent = billPerPerson;
}
bill.addEventListener('input', updateTotal);
totalPerPerson.addEventListener('input', updateTotal);

rayannn•2w ago

damm i was quite close, i think my flowchart was quite solid. its just that i lacked some parts like you showed i googled it a lot and couldnt find this solution so its frustrating to be stuck i honestly think i formulated it wrong and didnt get the right search results

Jochem•2w ago

it's a very common issue people have starting out, that they think that defining a variable will keep that variable updated as its components change 🙂 in reality, variables are (almost always) just postits that you write stuff on once and then can reuse places. Kinda like how the clipboard works on windows too, you copy a section of text and then change the original text, but the clipboard still has the old value

rayannn•2w ago

does putting it in a function automaticly keep updating it? since the code is the same right

Jochem•2w ago

well, the function runs multiple times. Every time the event is called, the code in the function executes that includes updating the value of the variable

rayannn•2w ago

ah right, otherwise you'd have to repeat it multiple times, now you can just call the function

Jochem•2w ago

yeah

rayannn•2w ago

il implement it later today and report back if i run into any problems, thanks for the help

Jochem•2w ago

no worries, glad to help!

rayannn•2w ago

It works in some way? it starts at NaN and then when i type it shows the number i put in. it often doesnt calculate and just gets stuck on NaN. its quire hard to replicate but it works in the end

Jochem•2w ago

oh, that's a good point! Change this line:

  totalPerPerson.textContent = billPerPerson;

  totalPerPerson.textContent = billPerPerson;

  totalPerPerson.textContent = billPerPerson || 0;

  totalPerPerson.textContent = billPerPerson || 0;

rayannn•2w ago

thank you, if i'd want to implement the reset button. i can just do a onclick function that resets everything to 0 right?

<button onclick(func)> Reset </button>
func delete (){
 bill.value = 0;
 amountOfPeople.value = 0;

}

<button onclick(func)> Reset </button>
func delete (){
 bill.value = 0;
 amountOfPeople.value = 0;

}

Jochem•2w ago

if your values are in a form, you can just have a <button type="reset"> in there. Or have an onclick that resets things manually, yeah

rayannn•2w ago

Whats the difference between using () on updatetotal and to leaving them out as you did in the example code

bill.addEventListener('input', updateTotal);
totalPerPerson.addEventListener('input', updateTotal);

bill.addEventListener('input', updateTotal);
totalPerPerson.addEventListener('input', updateTotal);

` vs

bill.addEventListener('input', updateTotal());
totalPerPerson.addEventListener('input', updateTotal());

bill.addEventListener('input', updateTotal());
totalPerPerson.addEventListener('input', updateTotal());

Jochem•2w ago

in the first example, you're passing a reference to the function to serve as the eventlistener, which will then be called each time the event fires in the second example, you're calling the function and passing the return value of that function to serve as the event listener. updateTotal doesn't return anything callable though, so the event listener will fail

rayannn•7d ago

that makes sense, thanks! it works and shows a 0.00 now, it often doesn't register/show the results while the labels are filled and other times it does. not sure why but it works so I'll put on solved

Jochem•7d ago

if you make a codepen, I can look at it though it might end up being tomorrow

rayannn•7d ago

its fine, the most important thing is that the DOM stuff works, il solve the small bugs later

Jochem•7d ago

kk 🙂

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How to display value or data in HTML with Javascript