bigint

1-js/99-js-misc/05-bigint/article.md

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+# BigInt
+
+[recent caniuse="bigint"]
+
+`BigInt` is a special numeric type that provides support for integers of arbitrary length.
+
+A bigint is created by appending `n` to the end of an integer literal or by calling the function `BigInt` that creates bigints from strings, numbers etc.
+
+```js
+const bigint = 1234567890123456789012345678901234567890n;
+
+const sameBigint = BigInt("1234567890123456789012345678901234567890");
+
+const bigintFromNumber = BigInt(10); // same as 10n
+```
+
+## Math operators
+
+`BigInt` can mostly be used like a regular number, for example:
+
+```js run
+alert(1n + 2n); // 3
+
+alert(5n / 2n); // 2
+```
+
+Please note: the division `5/2` returns the result rounded towards zero, without the decimal part. All operations on bigints return bigints.
+
+We can't mix bigints and regular numbers:
+
+```js run
+alert(1n + 2); // Error: Cannot mix BigInt and other types
+```
+
+We should explicitly convert them if needed: using either `BigInt()` or `Number()`, like this:
+
+```js run
+let bigint = 1n;
+let number = 2;
+
+// number to bigint
+alert(bigint + BigInt(number)); // 3
+
+// bigint to number
+alert(Number(bigint) + number); // 3
+```
+
+The conversion of bigint to number is always silent, but if the bigint is too huge and won't fit the number type, then extra bits will be cut off, causing a precision loss.
+
+````smart header="The unary plus is not supported on bigints"
+The unary plus operator `+value` is a well-known way to convert a `value` to number.
+
+On bigints it's not supported, to avoid confusion:
+```js run
+let bigint = 1n;
+
+alert( +bigint ); // error
+```
+````
+
+## Comparisons
+
+Comparisons, such as `<`, `>` work with bigints and numbers just fine:
+
+```js run
+alert( 2n > 1n ); // true
+
+alert( 2n > 1 ); // true
+```
+
+As numbers and bigints belong to different types, they can be equal `==`, but not strictly equal `===`:
+
+```js run
+alert( 1 == 1n ); // true
+
+alert( 1 === 1n ); // false
+```
+
+## Boolean operations
+
+When inside `if` or other boolean operations, bigints behave like numbers.
+
+For instance, in `if`, bigint `0n` is falsy, other values are truthy:
+
+```js run
+if (0n) {
+  // never executes
+}
+```
+
+Boolean operators, such as `||`, `&&` and others also work with bigints similar to numbers:
+
+```js run
+alert( 1n || 2 ); // 1
+
+alert( 0n || 2 ); // 2
+```
+
+## Polyfills
+
+Polyfilling bigints is tricky. The reason is that many JavaScript operators, such as `+`, `-` and so on behave differently with bigints compared to regular numbers.
+
+For example, division of bigints always returns an integer.
+
+To emulate such behavior, a polyfill would need to replace all such operators with its functions. But doing so is cumbersome and would cost a lot of performance.
+
+So, there's no well-known good polyfill.
+
+Although, the other way around is proposed by the developers of [https://github.com/GoogleChromeLabs/jsbi](JSBI) library.
+
+They suggest to use JSBI library calls instead of native bigints:
+
+| Operation | native `BigInt` | JSBI |
+|-----------|-----------------|------|
+| Creation from Number | `a = BigInt(789)` | `a = JSBI.BigInt(789)` |
+| Addition | `c = a + b` | `c = JSBI.add(a, b)` |
+| Subtraction	| `c = a - b` | `c = JSBI.subtract(a, b)` |
+| ... | ... | ... |
+
+...And then use the polyfill (Babel plugin) to convert JSBI calls to native bigints for those browsers that support them.
+
+In other words, this approach suggests that we write code in JSBI instead of native bigints. But JSBI works with numbers as with bigints internally, closely following the specification, so the code will be "bigint-ready".
+
+## References
+
+- [MDN docs on BigInt](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt).
+- [Specification](https://tc39.es/ecma262/#sec-bigint-objects).