How to Get Numeric Value from a Prompt Box

How to get numeric value from a prompt box?

parseInt() or parseFloat() are functions in JavaScript which can help you convert the values into integers or floats respectively.

Syntax:

 parseInt(string, radix);
 parseFloat(string);

string: the string expression to be parsed as a number.
radix: (optional, but highly encouraged) the base of the numeral system to be used - a number between 2 and 36.

Example:

 var x = prompt("Enter a Value", "0");
 var y = prompt("Enter a Value", "0");
 var num1 = parseInt(x);
 var num2 = parseInt(y);

After this you can perform which ever calculations you want on them.

Input as number in JavaScript prompt

No you can't customize the built-in browser prompt for security reasons.

Your best bet is to use a JavaScript library which offers such a feature like SweetAlert

You can create a number prompt like this:

swal({
    input: 'number',
    title: 'Enter a number',
}).then(function(result){
    alert("You picked number " + result.value);
});

Alternatively you could verify the user's input yourself and stick with prompt like this:

// need a way to check if input is a valid number
var isNumber = Number.isInteger || function(number){ return !isNaN(parseFloat(n)) && isFinite(n) }

var result = prompt("Enter your number");
if (!isNumber(result)){
   prompt("Please try again and enter your number");
}

I would strongly advice against using prompts as the user's browser will most likely block too many prompts in a row. Also keep in mind that the native prompt will block every other interaction a user can make with your side, you don't receive events and your UI won't update. Your website basically freezes until a user interacts with said prompt/alert/confirm.

Window.prompt accept only numeric values

You should reduce your code to the minimum required to reproduce the issue, e.g.:

 var selection = parseInt(window.prompt("Give the User Id:", "Type a number!"), 10);
if (selection != (/^[0-9.,]+$/)){  console.log('fail');} else {  console.log('pass');}

ReactJS: How To Get Input Value From The Prompt Box And Update It To Database

React this.setState, and useState does not make changes directly to the state object.

React this.setState, and React.useState create queues for React core to update the state object of a React component.

So the process to update React state is asynchronous for performance reasons. That’s why changes don’t feel immediate.

Try below code that's works !

function FoodListTable(props) {
  /* Definition of handleClick in component */
  const [newFoodName, setNewFoodName] = useState("");

  const handleEdit = () => {
    const enteredFood = prompt('Please enter your new food:');
    setNewFoodName(enteredFood);

    if (enteredFood) {
      Axios.put("https://mern-lefood.herokuapp.com/update", {
        newFoodName: enteredFood,
        id: props.val._id
      })
    }
  }

  return (
    <button onClick={handleEdit}>Edit</button>
  )
}

For more detail Click here

How to get a number to display in alert box rather than NAN

First take a value then perform every logic:

var feetMark = prompt('How tall is mark in feet?');
var lbsMark = prompt('How much does mark weigh in pounds?');


feetMark = parseFloat(feetMark);
lbsMark = parseFloat(lbsMark);

var kgMark = lbsMark / 2.2046;
var meterMark = feetMark / 3.2808;
var bmiMark = kgMark / (meterMark * meterMark);

alert('Mark is ' + ' ' + kgMark + ' '+ 'kilograms');
alert('Mark is ' + ' ' + meterMark + ' ' + 'meters');
alert('Marks BMI is ' + ' ' + bmiMark);

specify the variable type in the prompt

prompt is extremely basic and offers no way to constrain the input other than the way browsers do by default (e.g., no line breaks).

Instead, convert the string to number afterward. There are a lot of ways to do that:

Unary +: var jonage = +prompt("enter the johns age");
Number: var jonage = Number(prompt("enter the johns age"));
parseInt: var jonage = parseInt(prompt("enter the johns age"));
parseFloat: var jonage = parseFloat(prompt("enter the johns age"));

Unary `+` and `Number`:

...work the same way:

They convert the entire string to number if possible, yielding NaN if the entire string can't be converted to number. So +"123abc" is NaN.
They convert an empty string ("") to 0 (surprisingly).
They respect JavaScript syntax for specifying the number base (radix), so +"0x10" is 16 and +"0o10" is 8.

`parseInt`

Converts only as much of the string as it can before the first invalid character, not the whole string. So parstInt("123abc") is 123.
Converts an empty string ("") to NaN (not 0).
Respects JavaScript syntax for specifying the number base (radix), e.g., parseInt("0x10") is 16.
Also lets you specify the radix explicitly as a second argument, to force it to treat the input as being in that number base: parseInt("0x10", 10) is 0 (because the x becomes invalid, 0x is no longer treated as indicating the number base. This used to be important with decimal in case end users entered strings like "010" and browsers implemented "legacy" Octal (leading 0 instead of leading 0o), but it's been eight years now (since the 5th edition spec) since parseInt was officially not allowed to do that.
As the name suggests, only converts the part of the string that defines a whole number (integer).

`parseFloat`

Like parseInt, but does fractional numbers and doesn't do radix prefixes. parseFloat("0x16") is 0, because the x is invalid (because it doesn't do radix prefixes).

How to Get Numeric Value from a Prompt Box