capability.js
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exports.fetch = isFunction(global.fetch) && isFunction(global.ReadableStream)
exports.writableStream = isFunction(global.WritableStream)
exports.abortController = isFunction(global.AbortController)
exports.blobConstructor = false
try {
new Blob([new ArrayBuffer(1)])
exports.blobConstructor = true
} catch (e) {}
// The xhr request to example.com may violate some restrictive CSP configurations,
// so if we're running in a browser that supports `fetch`, avoid calling getXHR()
// and assume support for certain features below.
var xhr
function getXHR () {
// Cache the xhr value
if (xhr !== undefined) return xhr
if (global.XMLHttpRequest) {
xhr = new global.XMLHttpRequest()
// If XDomainRequest is available (ie only, where xhr might not work
// cross domain), use the page location. Otherwise use example.com
// Note: this doesn't actually make an http request.
try {
xhr.open('GET', global.XDomainRequest ? '/' : 'https://example.com')
} catch(e) {
xhr = null
}
} else {
// Service workers don't have XHR
xhr = null
}
return xhr
}
function checkTypeSupport (type) {
var xhr = getXHR()
if (!xhr) return false
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)
// If fetch is supported, then arraybuffer will be supported too. Skip calling
// checkTypeSupport(), since that calls getXHR().
exports.arraybuffer = exports.fetch || (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')
// If fetch is supported, then overrideMimeType will be supported too. Skip calling
// getXHR().
exports.overrideMimeType = exports.fetch || (getXHR() ? isFunction(getXHR().overrideMimeType) : false)
exports.vbArray = isFunction(global.VBArray)
function isFunction (value) {
return typeof value === 'function'
}
xhr = null // Help gc