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Just as a Blob is an opaque representation of data available on disk, an ArrayBuffer is an opaque representation of bytes available in memory.
The constructor takes one parameter, the length in bytes:
const buffer = new ArrayBuffer(64)
An ArrayBuffer value has one (read-only) property: byteLength, which - as the name suggests - expresses its length in bytes.
It also provides a slice() instance method which creates a new ArrayBuffer from an existing one, taking a starting position and an optional length:
const buffer = new ArrayBuffer(64)
const newBuffer = buffer.slice(32, 8)
Downloading data from the internet as an ArrayBuffer
We can download a blob from the internet and store it into an ArrayBuffer using XHR:
const downloadBlob = (url, callback) => {
const xhr = new XMLHttpRequest()
xhr.open('GET', url)
xhr.responseType = 'arraybuffer'
xhr.onload = () => {
callback(xhr.response)
}
xhr.send(null)
}