What are integers in JavaScript?
According to the ECMAScript specification, all numbers in JavaScript are floating-point. Yet, the notion of integer comes up occasionally. This blog post explains what it means.
JavaScript has only floating-point numbers. Integers appear internally in two ways. First, most JavaScript engines store a small enough number without a decimal fraction as an integer (with, for example, 31 bits) and maintain that representation as long as possible. They have to switch back to a floating point representation if a number’s magnitude grows too large or if a decimal fraction appears.
Internally, the following ranges of integers are important in JavaScript:
All blog posts on integers have the label jsint. Converting to integer is covered by two blog posts:
What are integers?
JavaScript has only floating-point numbers. Integers appear internally in two ways. First, most JavaScript engines store a small enough number without a decimal fraction as an integer (with, for example, 31 bits) and maintain that representation as long as possible. They have to switch back to a floating point representation if a number’s magnitude grows too large or if a decimal fraction appears.
Second, the ECMAScript specification has integer operators: namely, all of the bitwise operators. Those operators convert their operands to 32-bit integers and return 32-bit integers. For the specification, integer only means that the numbers don’t have a decimal fraction, and 32-bit means that they are within a certain range. For engines, 32-bit integer means that an actual integer (non-floating-point) representation can usually be introduced or maintained.
Ranges of integers
Internally, the following ranges of integers are important in JavaScript:
Safe integers [1], the largest practically usable range of integers that JavaScript supports:
- 53 bits plus a sign, range (−253, 253)
- Array indices [2]:
- 32 bits, unsigned
- Maximum length: 232−1
- Range of indices: [0, 232−1) (excluding the maximum length!)
Bitwise operands [3]:
- Unsigned right shift operator (>>>): 32 bits, unsigned, range [0, 232)
- All other bitwise operators: 32 bits, including a sign, range [−231, 231)
“Char codes”, UTF-16 code units as numbers:
- Accepted by String.fromCharCode()
- Returned by String.prototype.charCodeAt()
- 16 bit, unsigned
More blog posts on integers
All blog posts on integers have the label jsint. Converting to integer is covered by two blog posts:
- Converting to integer via shift operators: “Integers and shift operators in JavaScript”
- Converting to integer via parseInt(): “parseInt() doesn’t always correctly convert to integer”
References
- Safe integers in JavaScript
- Arrays in JavaScript
- Label bitwise_ops: blog posts on bitwise operators
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