The beginning of infinity in JavaScript

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Infinity begins relatively early in JavaScript:

    > Math.pow(2, 1024)
    Infinity
    > Math.pow(2, 1023)
    8.98846567431158e+307

What is going on here?


All numbers in JavaScript are floating point numbers and (roughly) encoded internally [1] as


1.f × 2p

This is the most common way of representing floating point numbers. The left-hand side of the multiplication comprises the digits, the right-hand side moves the dot to the correct position (to the left if it is negative, to the right if it is positive).


The mantissa is a binary 1, followed by a binary dot, followed by a 52 bit fraction f. The 11 bit exponent p has to be in the range


−1023 < p < 1024

Thus, the exponent of Math.pow(2, 1024) is out of range and Infinity is an error result.


Consult [1] if you want to know more about how numbers are encoded in JavaScript.

Reference




  1. How numbers are encoded in JavaScript


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