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 王天杨
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// Safari 6 and 6.1 for desktop, iPad, and iPhone are the only browsers that
// have WebKitMutationObserver but not un-prefixed MutationObserver.
// Must use `global` or `self` instead of `window` to work in both frames and web
// workers. `global` is a provision of Browserify, Mr, Mrs, or Mop.
/* globals self */
const scope = typeof global !== 'undefined' ? global : self
const BrowserMutationObserver =
(scope as any).MutationObserver || (scope as any).WebKitMutationObserver
export function makeRequestCallFromTimer(callback: () => void) {
return function requestCall() {
// We dispatch a timeout with a specified delay of 0 for engines that
// can reliably accommodate that request. This will usually be snapped
// to a 4 milisecond delay, but once we're flushing, there's no delay
// between events.
const timeoutHandle = setTimeout(handleTimer, 0)
// However, since this timer gets frequently dropped in Firefox
// workers, we enlist an interval handle that will try to fire
// an event 20 times per second until it succeeds.
const intervalHandle = setInterval(handleTimer, 50)
function handleTimer() {
// Whichever timer succeeds will cancel both timers and
// execute the callback.
clearTimeout(timeoutHandle)
clearInterval(intervalHandle)
callback()
}
}
}
// To request a high priority event, we induce a mutation observer by toggling
// the text of a text node between "1" and "-1".
export function makeRequestCallFromMutationObserver(callback: () => void) {
let toggle = 1
const observer = new BrowserMutationObserver(callback)
const node = document.createTextNode('')
observer.observe(node, { characterData: true })
return function requestCall() {
toggle = -toggle
;(node as any).data = toggle
}
}
export const makeRequestCall =
typeof BrowserMutationObserver === 'function'
? // MutationObservers are desirable because they have high priority and work
// reliably everywhere they are implemented.
// They are implemented in all modern browsers.
//
// - Android 4-4.3
// - Chrome 26-34
// - Firefox 14-29
// - Internet Explorer 11
// - iPad Safari 6-7.1
// - iPhone Safari 7-7.1
// - Safari 6-7
makeRequestCallFromMutationObserver
: // MessageChannels are desirable because they give direct access to the HTML
// task queue, are implemented in Internet Explorer 10, Safari 5.0-1, and Opera
// 11-12, and in web workers in many engines.
// Although message channels yield to any queued rendering and IO tasks, they
// would be better than imposing the 4ms delay of timers.
// However, they do not work reliably in Internet Explorer or Safari.
// Internet Explorer 10 is the only browser that has setImmediate but does
// not have MutationObservers.
// Although setImmediate yields to the browser's renderer, it would be
// preferrable to falling back to setTimeout since it does not have
// the minimum 4ms penalty.
// Unfortunately there appears to be a bug in Internet Explorer 10 Mobile (and
// Desktop to a lesser extent) that renders both setImmediate and
// MessageChannel useless for the purposes of ASAP.
// https://github.com/kriskowal/q/issues/396
// Timers are implemented universally.
// We fall back to timers in workers in most engines, and in foreground
// contexts in the following browsers.
// However, note that even this simple case requires nuances to operate in a
// broad spectrum of browsers.
//
// - Firefox 3-13
// - Internet Explorer 6-9
// - iPad Safari 4.3
// - Lynx 2.8.7
makeRequestCallFromTimer
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