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How to get a number value from an input field?
(4 answers)
Closed 1 year ago.
I've been losing my mind now for a couple of hours as I can't find out what I'm doing wrong here. Trying to see if the input is equal to 3, if so then show a window saying "The number is equal to 3".
Here's the HTML and Javascript:
<input type="number" name="number" id="number">
<button id="btn" onclick="checkNumber()">Button</button>
<div>
<span id="label"></span>
</div>
<script>
var number = document.getElementById("number").value;
function checkNumber() {
if (number === 3) {
window.alert("The number is equal to 3");
}
}
</script>
The number variable should typecasted, i.e converted to number type from string type
function checkNumber() {
var number = document.getElementById("number").value;
var value = Number(number);
if (value === 3) {
alert("The number is equal to 3");
} else {
alert("The number is not equal to 3");
}
}
<html>
<body>
<input id="number" name="number" type="number" />
<button id="btn" type="button" onclick="checkNumber()">Check</button>
</body>
</html>
Input value are strings, you can change them to number by adding "+" sign.
var number = document.getElementById("number");
function myFunc() {
if (+number.value === 3) {
window.alert("The number is equal to 3");
}
}
<input type="number" name="number" id="number">
<button id="btn" onclick="myFunc()">Button</button>
<div>
<span id="label"></span>
</div>
<script>
</script>
You are using === which checks both for type and value. the input received from the user is a string while 3 is a Number.
To solve that, you must first convert the input value to Number and then compare.
Also, i would add the reference for the element outside of the function and check for the current value each time the function gets called.
var element = document.getElementById("number");
function checkNumber() {
const numberAsString = element.value;
const number = Number(numberAsString);
if (number === 3) {
window.alert("The number is equal to 3");
}
}
<input type="number" name="number" id="number">
<button id="btn" onclick="checkNumber()">Button</button>
<div>
<span id="label"></span>
</div>
Related
I need to check if the value input in a HTML textbox contains a number, this is what I'm using so far, but it's not working, can anyone help? The text box would be a mix of letters and numbers, but I want to check if there are any numbers at all.
<input id="input" type="text">
<button onclick="myFunction()">Submit</button>
<p id="HasNumber"></p>
<script>
function myFunction() {
if (document.getElementById("input").value >= '0' && value <= '9' {
HasNumber.innerText = "Has Numbers" ; }
else {
HasNumber.innerText = "No Numbers" ; }
}
</script>
You can check if input contain number by using Regex like Below Example:
<input id="input" type="text">
<button onclick="myFunction()">Submit</button>
<p id="HasNumber"></p>
<script>
function myFunction() {
const inputVal = document.getElementById("input").value;
let matchPattern = inputVal.match(/\d+/g);
if (matchPattern != null) {
HasNumber.innerText = "Has Numbers" ;
} else {
HasNumber.innerText = "No Numbers" ;
}
}
</script>
Hello we were given a task where a user inputs any value up to 200 only and if it's a prime, it should print prime and if not, not prime. I already changed the code precisely. However, it's not working. Why is it so?
<!DOCTYPE html>
<html>
<body>
<script>
function doAction(){
//gets the value from the text field with id input1 and stores it in variable num1
var num1 = document.getElementById("input1").value;
//HINT: loop through some finite number and check whether they are prime
//You can create a function out of the CheckPrime exercise and use that to check if a number is
Prime
//for loop the numbers until you satisfy the num1
function primeprinter(num1) {
for(var i = 2; i < num1; i++)
if(num1 % i === 0) return false;
return num1 > 1;
if (primeprinter === true){
<p> Prime </p>
}
else{
<p> Not Prime </p>
}
}
//Challenges:
//validate if the input are numbers. Hint: Check out isNaN() function
//Validate the input to only be less than equal 200
}
</script>
<h2>Prime Numbers Printer</h2>
Prints the first N prime numbers. Only try up to 200.
<br/>
<br/>
Input1: <input type="text" id="input1"/>
<button type="button" onclick="doAction()">
Print Prime</button>
<br/>
<br/>
Result:
<p id="output"></p>
</body>
</html>
I am a beginner at javascript. Please help me ;-;
You can't inline HTML in JavaScript, i.e. if (primeprinter === true){ <p> Prime </p> } else { <p> Not Prime </p> } doesn't work. You could manipulate the DOM by hand.
function primeprinter(num1) {
for (let i = 2; i < num1; i++)
if (num1 % i === 0) return false;
return num1 > 1;
}
function doAction() {
const num1 = document.getElementById("input1").value;
document.getElementById("output").innerHTML = primeprinter(num1) ? "Prime" : "Not Prime";
}
<h2>Prime Numbers Printer</h2>
<span>Prints the first N prime numbers. Only try up to 200.</span>
<br />
<br />
<label for="input1">Input1: </label><input type="text" id="input1" />
<button type="button" onclick="doAction()">Print Prime</button>
<br />
<br />
<span>Result:</span>
<p id="output"></p>
I trying to make a calculator but I have the problem with the "dot" because give me advertisement like this...
"The specified value "." cannot be parsed, or is out of range."
This is my code...
numberDot.addEventListener('click', function() {
numberDot = '.' ;
input.value = input.value + numberDot;
console.log(typeof(input.value));
console.log(input.value);
});
This is one way to do it
Use type="number" inputs and radio buttons to choose the operation. That helps the person to enter numbers. You can also use type="text"
The important part is the conversion from string data into numeric values
When you read data from the value property of an input, the data is returned as a string. It can be converted to a number using parseInt (for integers) or parseFloat (for floating point). If it can't be parsed, NaN (Not a Number) is returned. To test for NaN, use isNaN().
For example:
let x = "kittens";
let n = parseInt(x);
if (isNaN(n)) {
console.log(x + " is not a number");
}
The important part of this example is the conversion of numbers and figuring out which operation to perform.
// get the elements in the DOM
let numberOne = document.getElementById("numberOne");
let numberTwo = document.getElementById("numberTwo");
let output = document.getElementById("output");
let calculator = document.getElementById("calculator");
// every time the calculator values change
calculator.addEventListener('change', function(evt) {
// get the values from the number inputs and try to convert them to floating point
let valueOne = parseFloat(numberOne.value);
let valueTwo = parseFloat(numberTwo.value);
// if both numbers are numbers (this is not 100% accurate)
if (!isNaN(valueOne) && !isNaN(valueTwo)) {
// create a variable to store the result
let value = 0;
// get the radio buttons
let ops = calculator['operation'];
// use the selected radio button to determine the operation
switch (ops.value) {
case '+':
value = valueOne + valueTwo;
break;
case '-':
value = valueOne - valueTwo;
}
// display the result
output.textContent = value;
}
});
<form id="calculator">
<!-- first number -->
<input id="numberOne" type="number" placeholder="1.0" step="0.01" min="0" max="10">
<br>
<!-- radio buttons for operations -->
<label for="add">Add
<input type="radio" name="operation" value="+">
</label>
<label for="subtract">Subtract
<input type="radio" name="operation" value="-">
</label>
<br>
<!-- second number -->
<input id="numberTwo" type="number" placeholder="1.0" step="0.01" min="0" max="10">
</form>
<!-- to display the result -->
<output id="output"></output>
For those who still end up here with the above error from the browser. Generally, you will get this error when inserting the string into the input field of the type number. Check the Input field type attribute. This should do the trick.
This code should detect where a number is above 1,000,000,000 and below 9,999,999,999. I try to input numbers between these 2 values, but it still returns the else statement. Where is the problem in this code?
<html>
<head>
<title>Checking with RegExp</title>
</head>
<body>
<p>Enter a 10 digit number between 1000000000 and 9999999999.</p>
<textarea id="inputnumber"></textarea>
<button type="button" id="submitnumber">Check</button>
<script>
function checknumber() {
var tendigitnum = document.getElementById("inputnumber")
if (tendigitnum >= 1000000000 && tendigitnum <= 9999999999) {
alert("You entered the number" + tendigitnum + ".")
}
else {
alert("The page will refresh. Please enter a valid number.")
location.reload()
}
}
document.getElementById("submitnumber").onclick = checknumber
</script>
</body>
</html>
You're comparing an HTML element to a number. You want to compare a number to a number, by:
Using the .value property on the element to get the string, and
Parsing that string to a number (you have lots of different ways to do this depending on your use case; see this answer for a list of them)
For instance:
var tendigitnum = Number(document.getElementById("inputnumber").value);
Live Example:
function checknumber() {
var tendigitnum = Number(document.getElementById("inputnumber").value)
if (tendigitnum >= 1000000000 && tendigitnum <= 9999999999) {
alert("You entered the number" + tendigitnum + ".")
} else {
alert("The page will refresh. Please enter a valid number.")
location.reload()
}
}
document.getElementById("submitnumber").onclick = checknumber
<p>Enter a 10 digit number between 1000000000 and 9999999999.</p>
<textarea id="inputnumber"></textarea>
<button type="button" id="submitnumber">Check</button>
On modern browsers you could use a number input:
<input type="number" id="inputnumber">
and use its valueAsNumber property instead of value, since valueAsNumber will already be a number. You can even add the range validation to the input. More on MDN.
You need to check the value in your element, in your code you are checking element
I've got simple form that has to return square root of a number. But i get NaN error. As you can see, variable "number" is number-type. What am i doing wrong?
let number = parseInt(document.getElementById('value'));
function myFunction() {
alert(Math.sqrt(number));
}
<div class="container">
<form>
<fieldset>
<legend>Number squared</legend>
<p><label >Insert number here: </label><input type="number" id="value"></p>
</fieldset>
<p><input type="button" id="button" onclick="myFunction()" value="calculate"></p>
</form>
</div>
First, document.getElementById() returns an HTML element. You would have to access the value property by doing document.getElementById().value. Second, the number variable will always be equal to NaN since that line of code is executed first and is never changed.
let value = document.getElementById('value').value // Evaluates to ""
let number = parseInt(value); // Evaluates to NaN
// The number variable is never re-evaluated when the function is invoked
function() {
alert(Math.sqrt(number));
}
You would have to move that line of code into your function so that the value of number is determined when the function is called, not at the beginning of code execution.
function myFunction() {
const number = parseInt(document.getElementById('value').value)
if (isNaN(number)) {
alert('Please pass in a number')
return
}
alert(Math.sqrt(number))
}
<div class="container">
<form>
<fieldset>
<legend>Number squared</legend>
<p><label>Insert number here: </label><input type="number" id="value"></p>
</fieldset>
<p><input type="button" id="button" onclick="myFunction()" value="calculate"></p>
</form>
</div>
function myFunction() {
const number = +document.getElementById('value').value;
if (isNaN(number)) {
alert('Please pass in a number')
return
}
alert(Math.sqrt(number))
}
It is because document.getElementById() returns the element itself and not the value. You need to get the value of the input to parse it as integer.
Change the code to parseInt(document.getElementById('value').value);
You must get your element value inside your function call, otherwise you will get NaN(Not a number), like this:
function myFunction() {
let number = parseInt(document.getElementById('value').value);
if(number !== "" && number != undefined && number != null && !isNaN(number)){
alert(Math.sqrt(number));
}else{
alert("Please enter valid number");
}
}
You can also check for undefined, null and empty string values.