I am just starting to learn Javascript and I immediately got confused by seemingly contradictory statements in Mozilla’s A re-introduction to JavaScript (JS tutorial).
One one hand:
“There’s no such thing as an integer in JavaScript, so you have to be a little careful with your arithmetic if you’re used to math in C or Java.”
On the other hand (immediately after that paragraph):
“In practice, integer values are treated as 32-bit ints (and are stored that way in some browser implementations), which can be important for bit-wise operations.”
and
“You can convert a string to an integer using the built-in parseInt() function.”
So, is there such thing as integer in JavaScript or isn’t there?
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Answer
UPDATE: with a new ES2020 standard released this answer is not entirely correct anymore, see the other answer (from @Mathias Lykkegaard Lorenzen) about BigInt details.
There is only the Number data type in JS that represents numbers.
Internally it is implemented as IEEE 754 double precision floating point number.
What it means is that – technically there is no dedicated data type that represents integer numbers.
Practically it means that we can safely use only numbers that are safely representable by the aforementioned standard. And it includes integer values in the range: [-9007199254740991; 9007199254740991]. Both values are defined as constants: Number.MIN_SAFE_INTEGER and Number.MAX_SAFE_INTEGER correspondingly.