I work in Javascript with integer numbers only (mainly adding numbers and shifting them). I wonder how big they can be without loosing any bits.

For example, how big `X`

can be such that `1 << X`

will represent `2^X`

?

All numbers in JavaScript are actually IEEE-754 compliant floating-point doubles. These have a 53-bit mantissa which should mean that any integer value with a magnitude of approximately 9 quadrillion or less -- more specifically, 9,007,199,254,740,991 -- will be represented accurately.

NOTICE: in 2018 main browsers and NodeJS are working also with the new Javascript's primitive-type, BigInt, solving the problems with integer value magnitude.

All answers are partially wrong - Maybe due the new ES6/ES7 specs - , read why:

First of all, in JavaScript, the representation of the number is **2^53 - 1** that is true for @Luke answer,
we can prove that by running `Number.MAX_SAFE_INTEGER`

that will show a big number, then we do `log2`

to confirm that the number of bits is the same :

```
Number.MAX_SAFE_INTEGER
9007199254740991
Math.log2(9007199254740991)
53
```

Welcome to Javascript!

All numbers in JavaScript are 64-bit (double-precision) floating point numbers.

Here's a description of the format and what values can and can't be represented with it.

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