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| 1 | +/* @flow */ |
| 2 | +/* globals MessageChannel */ |
| 3 | + |
| 4 | +import { noop } from 'shared/util' |
| 5 | +import { handleError } from './error' |
| 6 | +import { isIOS, isNative } from './env' |
| 7 | + |
| 8 | +const callbacks = [] |
| 9 | +let pending = false |
| 10 | + |
| 11 | +function flushCallbacks () { |
| 12 | + pending = false |
| 13 | + const copies = callbacks.slice(0) |
| 14 | + callbacks.length = 0 |
| 15 | + for (let i = 0; i < copies.length; i++) { |
| 16 | + copies[i]() |
| 17 | + } |
| 18 | +} |
| 19 | + |
| 20 | +// Here we have async deferring wrappers using both micro and macro tasks. |
| 21 | +// In < 2.4 we used micro tasks everywhere, but there are some scenarios where |
| 22 | +// micro tasks have too high a priority and fires in between supposedly |
| 23 | +// sequential events (e.g. #4521, #6690) or even between bubbling of the same |
| 24 | +// event (#6566). However, using macro tasks everywhere also has subtle problems |
| 25 | +// when state is changed right before repaint (e.g. #6813, out-in transitions). |
| 26 | +// Here we use micro task by default, but expose a way to force macro task when |
| 27 | +// needed (e.g. in event handlers attached by v-on). |
| 28 | +let microTimerFunc |
| 29 | +let macroTimerFunc |
| 30 | +let useMacroTask = false |
| 31 | + |
| 32 | +// Determine (macro) Task defer implementation. |
| 33 | +// Technically setImmediate should be the ideal choice, but it's only available |
| 34 | +// in IE. The only polyfill that consistently queues the callback after all DOM |
| 35 | +// events triggered in the same loop is by using MessageChannel. |
| 36 | +/* istanbul ignore if */ |
| 37 | +if (typeof setImmediate !== 'undefined' && isNative(setImmediate)) { |
| 38 | + macroTimerFunc = () => { |
| 39 | + setImmediate(flushCallbacks) |
| 40 | + } |
| 41 | +} else if (typeof MessageChannel !== 'undefined' && ( |
| 42 | + isNative(MessageChannel) || |
| 43 | + // PhantomJS |
| 44 | + MessageChannel.toString() === '[object MessageChannelConstructor]' |
| 45 | +)) { |
| 46 | + const channel = new MessageChannel() |
| 47 | + const port = channel.port2 |
| 48 | + channel.port1.onmessage = flushCallbacks |
| 49 | + macroTimerFunc = () => { |
| 50 | + port.postMessage(1) |
| 51 | + } |
| 52 | +} else { |
| 53 | + macroTimerFunc = () => { |
| 54 | + setTimeout(flushCallbacks, 0) |
| 55 | + } |
| 56 | +} |
| 57 | + |
| 58 | +// Determine MicroTask defer implementation. |
| 59 | +// $flow-disable-line, istanbul ignore next |
| 60 | +if (typeof Promise !== 'undefined' && isNative(Promise)) { |
| 61 | + const p = Promise.resolve() |
| 62 | + microTimerFunc = () => { |
| 63 | + p.then(flushCallbacks) |
| 64 | + // in problematic UIWebViews, Promise.then doesn't completely break, but |
| 65 | + // it can get stuck in a weird state where callbacks are pushed into the |
| 66 | + // microtask queue but the queue isn't being flushed, until the browser |
| 67 | + // needs to do some other work, e.g. handle a timer. Therefore we can |
| 68 | + // "force" the microtask queue to be flushed by adding an empty timer. |
| 69 | + if (isIOS) setTimeout(noop) |
| 70 | + } |
| 71 | +} else { |
| 72 | + // fallback to macro |
| 73 | + microTimerFunc = macroTimerFunc |
| 74 | +} |
| 75 | + |
| 76 | +/** |
| 77 | + * Wrap a function so that if any code inside triggers state change, |
| 78 | + * the changes are queued using a Task instead of a MicroTask. |
| 79 | + */ |
| 80 | +export function withMacroTask (fn: Function): Function { |
| 81 | + return fn._withTask || (fn._withTask = function () { |
| 82 | + useMacroTask = true |
| 83 | + const res = fn.apply(null, arguments) |
| 84 | + useMacroTask = false |
| 85 | + return res |
| 86 | + }) |
| 87 | +} |
| 88 | + |
| 89 | +export function nextTick (cb?: Function, ctx?: Object): ?Promise { |
| 90 | + let _resolve |
| 91 | + callbacks.push(() => { |
| 92 | + if (cb) { |
| 93 | + try { |
| 94 | + cb.call(ctx) |
| 95 | + } catch (e) { |
| 96 | + handleError(e, ctx, 'nextTick') |
| 97 | + } |
| 98 | + } else if (_resolve) { |
| 99 | + _resolve(ctx) |
| 100 | + } |
| 101 | + }) |
| 102 | + if (!pending) { |
| 103 | + pending = true |
| 104 | + if (useMacroTask) { |
| 105 | + macroTimerFunc() |
| 106 | + } else { |
| 107 | + microTimerFunc() |
| 108 | + } |
| 109 | + } |
| 110 | + // $flow-disable-line |
| 111 | + if (!cb && typeof Promise !== 'undefined') { |
| 112 | + return new Promise(resolve => { |
| 113 | + _resolve = resolve |
| 114 | + }) |
| 115 | + } |
| 116 | +} |
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