标签:snat fine catch res ++ string ring def cti
源码:
const callbacks = [] let pending = false function flushCallbacks () { pending = false const copies = callbacks.slice(0) callbacks.length = 0 for (let i = 0; i < copies.length; i++) { copies[i]() } } let timerFunc if (typeof Promise !== ‘undefined‘ && isNative(Promise)) { const p = Promise.resolve() timerFunc = () => { p.then(flushCallbacks) if (isIOS) setTimeout(noop) } isUsingMicroTask = true } else if (!isIE && typeof MutationObserver !== ‘undefined‘ && ( isNative(MutationObserver) || MutationObserver.toString() === ‘[object MutationObserverConstructor]‘ )) { let counter = 1 const observer = new MutationObserver(flushCallbacks) const textNode = document.createTextNode(String(counter)) observer.observe(textNode, { characterData: true }) timerFunc = () => { counter = (counter + 1) % 2 textNode.data = String(counter) } isUsingMicroTask = true } else if (typeof setImmediate !== ‘undefined‘ && isNative(setImmediate)) { timerFunc = () => { setImmediate(flushCallbacks) } } else { timerFunc = () => { setTimeout(flushCallbacks, 0) } } export function nextTick (cb?: Function, ctx?: Object) { let _resolve callbacks.push(() => { if (cb) { try { cb.call(ctx) } catch (e) { handleError(e, ctx, ‘nextTick‘) } } else if (_resolve) { _resolve(ctx) } }) if (!pending) { pending = true timerFunc() } if (!cb && typeof Promise !== ‘undefined‘) { return new Promise(resolve => { _resolve = resolve }) } }
总体来说:就是先判断是否支持promise,如果支持promise。就通过Promise.resolve的方法,异步执行方法,如果不支持promise,就判断是否支持MutationObserver。如果支持,就通过MutationObserver(微异步)来异步执行方法,如果MutationObserver还不支持,就通过setTimeout来异步执行方法。
MutaionObserver通过创建新的节点,调用timerFunc方法,改变MutationObserver监听的节点变化,从而触发异步方法执行。
标签:snat fine catch res ++ string ring def cti
原文地址:https://www.cnblogs.com/yaxinwang/p/13827530.html