capability.js

exports.fetch = isFunction(global.fetch) && isFunction(global.ReadableStream)

exports.blobConstructor = false
try {
	new Blob([new ArrayBuffer(1)])
	exports.blobConstructor = true
} catch (e) {}

var xhr = new global.XMLHttpRequest()
// If location.host is empty, e.g. if this page/worker was loaded
// from a Blob, then use example.com to avoid an error
xhr.open('GET', global.location.host ? '/' : 'https://example.com')

function checkTypeSupport (type) {
	try {
		xhr.responseType = type
		return xhr.responseType === type
	} catch (e) {}
	return false
}

// For some strange reason, Safari 7.0 reports typeof global.ArrayBuffer === 'object'.
// Safari 7.1 appears to have fixed this bug.
var haveArrayBuffer = typeof global.ArrayBuffer !== 'undefined'
var haveSlice = haveArrayBuffer && isFunction(global.ArrayBuffer.prototype.slice)

exports.arraybuffer = haveArrayBuffer && checkTypeSupport('arraybuffer')
// These next two tests unavoidably show warnings in Chrome. Since fetch will always
// be used if it's available, just return false for these to avoid the warnings.
exports.msstream = !exports.fetch && haveSlice && checkTypeSupport('ms-stream')
exports.mozchunkedarraybuffer = !exports.fetch && haveArrayBuffer &&
	checkTypeSupport('moz-chunked-arraybuffer')
exports.overrideMimeType = isFunction(xhr.overrideMimeType)
exports.vbArray = isFunction(global.VBArray)

function isFunction (value) {
  return typeof value === 'function'
}

xhr = null // Help gc