How to determine if a number is infinite using Javascript?

Question

There is the possibility to check if a certain value is a infinite number using Javascript?

Answer 1

You can use the function isFinite():

console.log(!isFinite(Number.MAX_SAFE_INTEGER)); // false
console.log(!isFinite(Infinity));                // true

Another way is to compare the value with Number.POSITIVE_INFINITY and Number.NEGATIVE_INFINITY:

if (numero == Number.POSITIVE_INFINITY || numero == Number.NEGATIVE_INFINITY) {
    alert('Número infinito!');
} else {
    alert('Número finito!')
}

Answer 2

Apart from the example of the other answer that got very good, you can also do so:

var n = ...; //Valor infinito ou não
var isInfinite = (!isNaN(n) && !isFinite(n));

console.log(isInfinite);

The isNaN is to prevent chance !isFinite(n); return true chance to receive a number NaN

Could move to a function to facilitate:

function isInfinite(num) {
    return !isNaN(num) && !isFinite(num);
}

Or

function isInfinite(num) {
     return num == Number.POSITIVE_INFINITY ||
            num == Number.NEGATIVE_INFINITY;
}

The use would look like this:

alert(isInfinite(numero));

Yet I read in the first issue that you used a number like this: 100000000000000000000000000000100000000000000000000000000000, actually this is not infinite, this would be a number that exceeds the limit

A simple test:

function checkNumberSizeValide(num) {
    return num <= Number.MAX_SAFE_INTEGER;
}

function isInfinite2(num) {
     return num == Number.POSITIVE_INFINITY ||
            num == Number.NEGATIVE_INFINITY;
}

var valor = window.prompt("Digite um numero, pode ser inteiro ou quebrado, exemplo 1.0000002");

if (/^(\d+|\d+[.]\d+)$/.test(valor)) {
    valor = Number(valor);

    console.log("valor", valor);

    console.log("O numero é valido dentro do limite máximo:", checkNumberSizeValide(valor));
} else {
    alert("Digite um numero");
}