-
路由 简单来说路由就是用来跟后端服务器进行交互的一种方式，通过不同的路径，来请求不同的资源，请求不同的页面是路由的其中一种功能。
-
实现原理 是基于html5 特性 history.pushState实现的 history.pushState & history.replaceState 都是添加或修改历史记录条目， 在不刷新页面的情况下
-
使用方法
let stateObj = {
foo: "bar",
};
history.pushState(stateObj, "page 2", "bar.html");
在前端使用路由要有个前提，那就是后端要将全部的路径都指向首页，即 index.html。否则后端会出现 404 错误。
- 定义（引用官网
原文：当你设置 vm.someData = 'new value'，该组件不会立即重新渲染。当刷新队列时，组件会在下一个事件循环“tick”中更新。 个人理解：dom更新是异步的，nextTick为该次事件循环后的回调钩子，确保了dom更新完毕，可以在nextTick中对更新后的dom进行操作
vm.someData = 'new value'
//someData 未更新
Vue.nextTick(function(){
//someData更新了
})
（ps: $nextTick 返回一个Promise对象）
- 异步更新队列
数据变化时，Vue开启一个队列，缓存同一循环事件中所有的dom更新，即同一watcher更新多次时，有且仅有一个入队列，避免了不必要的计算和dom更新
- 源码
/**
* Defer a task to execute it asynchronously.
*/
export const nextTick = (function () {
const callbacks = []
let pending = false
let timerFunc
function nextTickHandler () {
pending = false
const copies = callbacks.slice(0)
callbacks.length = 0
for (let i = 0; i < copies.length; i++) {
copies[i]()
}
}
// the nextTick behavior leverages the microtask queue, which can be accessed
// via either native Promise.then or MutationObserver.
// MutationObserver has wider support, however it is seriously bugged in
// UIWebView in iOS >= 9.3.3 when triggered in touch event handlers. It
// completely stops working after triggering a few times... so, if native
// Promise is available, we will use it:
/* istanbul ignore if */
if (typeof Promise !== 'undefined' && isNative(Promise)) {
var p = Promise.resolve()
var logError = err => { console.error(err) }
timerFunc = () => {
p.then(nextTickHandler).catch(logError)
// in problematic UIWebViews, Promise.then doesn't completely break, but
// it can get stuck in a weird state where callbacks are pushed into the
// microtask queue but the queue isn't being flushed, until the browser
// needs to do some other work, e.g. handle a timer. Therefore we can
// "force" the microtask queue to be flushed by adding an empty timer.
if (isIOS) setTimeout(noop)
}
} else if (!isIE && typeof MutationObserver !== 'undefined' && (
isNative(MutationObserver) ||
// PhantomJS and iOS 7.x
MutationObserver.toString() === '[object MutationObserverConstructor]'
)) {
// use MutationObserver where native Promise is not available,
// e.g. PhantomJS, iOS7, Android 4.4
var counter = 1
var observer = new MutationObserver(nextTickHandler)
var textNode = document.createTextNode(String(counter))
observer.observe(textNode, {
characterData: true
})
timerFunc = () => {
counter = (counter + 1) % 2
textNode.data = String(counter)
}
} else {
// fallback to setTimeout
/* istanbul ignore next */
timerFunc = () => {
setTimeout(nextTickHandler, 0)
}
}
return function queueNextTick (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, reject) => {
_resolve = resolve
})
}
}
})()
-
callbacks 存放 nextTick 回调函数
-
nextTickHandler 用于挨个触发callbacks里的每个回调
-
timerFunc 根据浏览器支持情况（Promise/MutationObserver/setTimeout）将nextTickHandler封装延时函数（会在同步任务以及更新DOM的异步任务之后回调具体函数。）
-
queueNextTick 作为钩子函数对外暴露，接受callback、context(上下文执行环境)，如若不传入任何参数，则返回一个新的Promise对象
这篇写的很详细 Vue的computed和watch的细节全面分析