problem with number () javascript

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problem with number () javascript

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#1 by (3 votes)
#2 by (3 votes)
#3 by (2 votes)

-1

Someone knows why

Number(4444444444444444); // (tiene 16 cuatros)

results in

4444444444444444

but

Number(44444444444444444); // (tiene 17 cuatros)

results in

44444444444444450

javascript

asked by jufrfa 06.09.2017 в 23:45

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3 answers

3

The largest number that can be stored (with precision) in JavaScript is 9007199254740992. The reason why it returns 44444444444444450 is because the JavaScript engine makes an attempt to represent and approximate the value provided.

Then

Number(4444444444444444) = 4444444444444444 (OK, porque es menor al valor maximo permitido) 
Number(44444444444444444) = 44444444444444450 (WRONG, porque es mayor al valor maximo permitido)

If you are interested, check out this link link so you can understand in detail how the representation of numbers works.

Greetings Juan Simón

answered by 07.09.2017 в 00:53

3

According to the Number documentation, Integers (numbers without a period or exponent notation) are accurate up to 15 digits. link

For example:

var x = 999999999999999;   // x sera 999999999999999
var y = 9999999999999999;  // y sera 10000000000000000

answered by 07.09.2017 в 00:59

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score 2 · Accepted Answer

The problem

The problem is that:

Number(44444444444444444);

Exceeds the maximum allowed by Javascript for object Number . There is a constant that calculates this value and you can obtain it with:

Number.MAX_VALUE;

So if you do this:

    var biggestNum = Number.MAX_VALUE;
    console.log("Máximo admitido: "+ biggestNum);

You will get this on screen:

    Máximo admitido: 1.7976931348623157e+308

For the same reason explained in (1), Number(44444444444444444) is not a safeInteger , that is, it is not an integer on which you can operate without risk of error .

To check if an integer is safe, Javascript has the function Number.isSafeInteger

So if you do this to verify your number:

    console.log(Number.isSafeInteger(44444444444444444));

You will get this:

    false

Moreover, the same maximum allowed for integers in JS is not safe. If we do:

console.log(Number.isSafeInteger(Number.MAX_VALUE));

We will get:

     false

The solution

To operate with large numbers you have two exits:

Implement a third-party library managed by bigInteger. For example:

Wait for Javascript to include BigInteger objects

Fragment of code testing what was affirmed in this answer

//1. Máximo admitido
var biggestNum = Number.MAX_VALUE;
console.log("Máximo admitido: "+ biggestNum);


//2. 
tuNumero=Number(44444444444444444);
console.log("¿Tú número es safeInteger? "+Number.isSafeInteger(tuNumero));

// 3.
console.log("¿El máximo admitido es safeInteger? "+Number.isSafeInteger(biggestNum));