I am trying to build a calorie calculator using HTML and JS and am currently struggling to show the output on screen (or via console.log). I know I'm doing something very basic quite wrong but can't currently pinpoint what that is.
Here's both my HTML and JS code below:
document.getElementById("bmrForm").addEventListener("submit", calcBMR);
function calcBMR(gender, weightKG, heightCM, age) {
// Calculate BMR
if (gender = 'male') {
let BMR = 10 * weightKG + 6.25 * heightCM - 5 * age + 5;
} else {
let BMR = 10 * weightKG + 6.25 * heightCM - 5 * age - 161;
}
console.log(BMR);
} <body>
<script src="./script.js"></script>
<section>
<form id="bmrForm" onsubmit="calcBMR()">
<input type="text" id="gender" placeholder="Male or female?">
<input type="number" id="weight" placeholder="Weight in KG">
<input type="number" id="height" placeholder="Height in CM">
<input type="number" id="age" placeholder="How old are you?">
<button type="submit" id="submitBtn">Do Magic!</button>
</form>
<p id="output">0</p>
</section>
</body>Try this one, you are almost done, just by getting value from the input when user clicks the button.
But I have to notice you that submit button will immediately redirect to a new page, you should use click instead if you want to show yourself result.
document.getElementById("submitBtn").addEventListener("click",function(){
let gen = document.querySelector('#gender').value
let weight = document.querySelector('#weight').value
let height = document.querySelector('#height').value
let ages = document.querySelector('#age').value
calcBMR(gen,weight,height,ages)
})
function calcBMR(gender, weightKG, heightCM, age) {
let BMR
// Calculate BMR
if (gender = 'male') {
BMR = 10 * weightKG + 6.25 * heightCM - 5 * age + 5;
} else {
BMR = 10 * weightKG + 6.25 * heightCM - 5 * age - 161;
}
document.querySelector('#output').textContent = BMR;
}<body>
<script src="./script.js"></script>
<section>
<form id="bmrForm">
<input type="text" id="gender" placeholder="Male or female?">
<input type="number" id="weight" placeholder="Weight in KG">
<input type="number" id="height" placeholder="Height in CM">
<input type="number" id="age" placeholder="How old are you?">
<button id="submitBtn">Do Magic!</button>
</form>
<p id="output">0</p>
</section>
</body>You can remove the line document.getElementById("bmrForm").addEventListener("submit", calcBMR);
You can pass event to onsubmit - <form id="bmrForm" onsubmit="calcBMR(event)">
function calcBMR(e) {
e.preventDefault();
var elements = document.getElementById("bmrForm").elements; // logic to get all form elements
var obj ={};
for(var i = 0 ; i < elements.length ; i++){
var item = elements.item(i);
obj[item.id] = item.value;
}
const {gender, weight, height, age } = obj; //Get values from obj
// Calculate BMR
let BMR = '';
if (gender === 'male') {
BMR = 10 * weight + 6.25 * height - 5 * age + 5;
} else {
BMR = 10 * weight + 6.25 * height - 5 * age - 161;
}
console.log(BMR);
}
Several things need to be modified in order to achieve your desired result.
document.getElementById("bmrForm").addEventListener("submit", calcBMR); is not needed because we can pass in a function directly to the onsubmit attribute of the form element.gender, weightKG, heightCM, and age parameters are not automatically passed in to the calcBMR function. The values need to be retrieved from the document.BMR variable needs to be defined above the if/else block because of scoping.return statement needs to be added to the onsubmit attribute so that the form does not submit and refresh the page. Alternatively, if the desired effect is to update the text on the screen, a button element with a click event handler added to it may be a better option that a form with a submit handler.== or === in JavaScript. Therefore, the gender = 'male' part needs to be changed to gender === 'male'.textContent can be changed with document.getElementById("output").textContent = BMR.Below is the code with the changes listed above.
function calcBMR() {
let gender = document.getElementById("gender").value;
let weightKG = document.getElementById("weight").value;
let heightCM = document.getElementById("height").value;
let age = document.getElementById("age").value;
let BMR;
// Calculate BMR
if (gender === 'male') {
BMR = 10 * weightKG + 6.25 * heightCM - 5 * age + 5;
} else {
BMR = 10 * weightKG + 6.25 * heightCM - 5 * age - 161;
}
console.log(BMR);
document.getElementById("output").textContent = BMR;
return false;
}<body>
<script src="./script.js"></script>
<section>
<form id="bmrForm" onsubmit="return calcBMR()">
<input type="text" id="gender" placeholder="Male or female?">
<input type="number" id="weight" placeholder="Weight in KG">
<input type="number" id="height" placeholder="Height in CM">
<input type="number" id="age" placeholder="How old are you?">
<button type="submit" id="submitBtn">Do Magic!</button>
</form>
<p id="output">0</p>
</section>The BMR is in the if tree, it must be in parent.
Try this!
document.getElementById("bmrForm").addEventListener("submit", calcBMR);
const output = document.getElementById('output');
function calcBMR(event) {
// Get the [gender, weightKG, heightCM, age] value
let gender = document.getElementById('gender').value;
let weightKG = document.getElementById('weight').value;
let heightCM = document.getElementById('height').value;
let age = document.getElementById('age').value;
// Set default BMR to 0
let BMR = 0;
// Calculate BMR
if (gender = 'male') {
BMR = 10 * weightKG + 6.25 * heightCM - 5 * age + 5;
} else {
BMR = 10 * weightKG + 6.25 * heightCM - 5 * age - 161;
}
console.log(BMR);
output.innerText = BMR;
// Cancel form submit
event.preventDefault();
return;
}<body>
<script src="./script.js"></script>
<section>
<form id="bmrForm">
<input type="text" id="gender" placeholder="Male or female?">
<input type="number" id="weight" placeholder="Weight in KG">
<input type="number" id="height" placeholder="Height in CM">
<input type="number" id="age" placeholder="How old are you?">
<button type="submit" id="submitBtn">Do Magic!</button>
</form>
<p id="output">0</p>
</section>
</body>I used a selector instead of the text field for the gender.
I used form.elements to get the values from the form.
I used event.preventDefault(); to prevent the form from redirecting on submit.
// your form
var form = document.getElementById("formId");
var DoMagic = function(event)
{
event.preventDefault();
var elements = form.elements;
if (elements["gender"].value == "male")
{
var result = 10 * elements["weight"].value + 6.25 * elements["height"].value - 5 * elements["age"].value + 5;
}
else
{
var result = 10 * elements["weight"].value + 6.25 * elements["height"].value - 5 * elements["age"].value - 161;
}
document.getElementById("result").textContent = "Result: " + result;
}
// attach event listener
form.addEventListener("submit", DoMagic, true);<form id = "formId">
<label>Gender</label>
<select name="gender">
<option value="male">Male</option>
<option value="female">Female</option>
</select>
<br>
<label>Weight (kg)</label>
<input name="weight" type="number">
<br>
<label>Height (cm)</label>
<input name="height" type="number">
<br>
<label>Age (years)</label>
<input name="age" type="number">
<br>
<input type="submit" value="Do Magic!">
</form>
<span id='result'> </span>Working Codepen
There are a few fundamental flaws in your code. Having said that, studying this will really give you a proper understanding of Javascript.
HTML:
<body>
<section>
<form id="bmrForm">
<input type="text" id="gender" placeholder="Male or female?" name="gender">
<input type="number" id="weight" placeholder="Weight in KG" name="weight">
<input type="number" id="height" placeholder="Height in CM" name="height">
<input type="number" id="age" placeholder="How old are you?" name="age">
<button type="submit" id="submitBtn">Do Magic!</button>
</form>
<p id="output">0</p>
</section>
</body>
Javascript:
document.getElementById("bmrForm").addEventListener("submit", calcBMR);
const output = document.querySelector('#output')
function calcBMR(e) {
e.preventDefault();
output.innerText = ''
const formData = new FormData(e.target)
const { age, gender, height, weight} = Object.fromEntries(formData);
let BMR = 0
// Calculate BMR
if (gender === 'male') {
BMR = 10 * parseInt(weight) + 6.25 * parseInt(height) - 5 * parseInt(age) + 5;
} else {
BMR = 10 * parseInt(weight) + 6.25 * parseInt(height) - 5 * parseInt(age) - 161;
}
output.innerText = BMR
}