Binary data in JavaScript is implemented in a non-standard way, compared to other languages. But when we sort things out, everything becomes fairly simple.
- **`Uint8Array`** -- treats each byte in `ArrayBuffer` as a separate number, with possible values from 0 to 255 (a byte is 8-bit, so it can hold only that much). Such value is called a "8-bit unsigned integer".
- **`Uint16Array`** -- treats every 2 bytes as an integer, with possible values from 0 to 65535. That's called a "16-bit unsigned integer".
- **`Uint32Array`** -- treats every 4 bytes as an integer, with possible values from 0 to 4294967295. That's called a "32-bit unsigned integer".
- **`Float64Array`** -- treats every 8 bytes as a floating point number with possible values from <code>5.0x10<sup>-324</sup></code> to <code>1.8x10<sup>308</sup></code>.
So, the binary data in an `ArrayBuffer` of 16 bytes can be interpreted as 16 "tiny numbers", or 8 bigger numbers (2 bytes each), or 4 even bigger (4 bytes each), or 2 floating-point values with high precision (8 bytes each).
The common term for all these views (`Uint8Array`, `Uint32Array`, etc) is [TypedArray](https://tc39.github.io/ecma262/#sec-typedarray-objects). They share the same set of methods and properities.
Please note, there's no constructor called `TypedArray`, it's just a common "umbrella" term to represent one of views over `ArrayBuffer`: `Int8Array`, `Uint8Array` and so on, the full list will soon follow.
Optionally we can provide `byteOffset` to start from (0 by default) and the `length` (till the end of the buffer by default), then the view will cover only a part of the `buffer`.
3. If another `TypedArray` is supplied, it does the same: creates a typed array of the same length and copies values. Values are converted to the new type in the process, if needed.
4. For a numeric argument `length` -- creates the typed array to contain that many elements. Its byte length will be `length` multiplied by the number of bytes in a single item `TypedArray.BYTES_PER_ELEMENT`:
5. Without arguments, creates an zero-length typed array.
We can create a `TypedArray` directly, without mentioning `ArrayBuffer`. But a view cannot exist without an underlying `ArrayBuffer`, so gets created automatically in all these cases except the first one (when provided).
To access the `ArrayBuffer`, there are properties:
- `arr.buffer` -- references the `ArrayBuffer`.
- `arr.byteLength` -- the length of the `ArrayBuffer`.
For instance, let's try to put 256 into `Uint8Array`. In binary form, 256 is `100000000` (9 bits), but `Uint8Array` only provides 8 bits per value, that makes the available range from 0 to 255.
For bigger numbers, only the rightmost (less significant) 8 bits are stored, and the rest is cut off:
`Uint8ClampedArray` is special in this aspect, its behavior is different. It saves 255 for any number that is greater than 255, and 0 for any negative number. That behavior is useful for image processing.
`TypedArray` has regular `Array` methods, with notable exceptions.
We can iterate, `map`, `slice`, `find`, `reduce` etc.
There are few things we can't do though:
- No `splice` -- we can't "delete" a value, because typed arrays are views on a buffer, and these are fixed, contiguous areas of memory. All we can do is to assign a zero.
- `arr.subarray([begin, end])` creates a new view of the same type from `begin` to `end` (exclusive). That's similar to `slice` method (that's also supported), but doesn't copy anything -- just creates a new view, to operate on the given piece of data.
[DataView](mdn:/JavaScript/Reference/Global_Objects/DataView) is a special super-flexible "untyped" view over `ArrayBuffer`. It allows to access the data on any offset in any format.
- With `DataView` we access the data with methods like `.getUint8(i)` or `.getUint16(i)`. We choose the format at method call time instead of the construction time.
`DataView` is great when we store mixed-format data in the same buffer. For example, when we store a sequence of pairs (16-bit integer, 32-bit float), `DataView` allows to access them easily.
In most cases we create and operate directly on typed arrays, leaving `ArrayBuffer` under cover, as a "common denominator". We can access it as `.buffer` and make another view if needed.
We'll see these terms in the next chapters. `BufferSource` is one of the most common terms, as it means "any kind of binary data" -- an `ArrayBuffer` or a view over it.
