[Compilation and sharing] Some vue-router related interview questions (with answer analysis)-Vue.js-php.cn

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[Compilation and sharing] Some vue-router related interview questions (with answer analysis)

The principle of vue-router

In a single-page application, switching between different components needs to be implemented through front-end routing .

Front-end routing

1.key is the path, value is the component, used to display the page content
2. Working process: when the browser's path changes , the corresponding component will be displayed.
vue-router’s routing function: Map components to routes and then render them

Mainly

How to change the URL without causing the page to refresh
How to detect the URL change [Related recommendations: vuejs video tutorial, web front-end development 】

The hash pattern of the route

hash is the ## in the URL ## and the following part, the URL after # will not be sent to the server, so changing the hash part in the URL will not cause the page to refresh
Window can monitor
onhashchange event changes. When the hash changes, read the content after #, match routing rules based on the information, and change the page routing by changing window.location.hash.

Three ways to change the URL

Change the URL through tags
Change the URL through window.location

Advantages

Good compatibility, all browsers can support it
Changes in the hash value will not send requests to the backend, it is completely front-end routing

##Disadvantages

The hash value needs to be preceded by #, which does not comply with the url specification and is not beautiful

routing history mode - using the new pushState() and replaceState()## in the history interface of H5's history API

#html5 # Method, used to add and modify records in the browsing history, change the page path, so that the URL jump will not reload the page.
The
event is similar to the
hashchange event, but the popstate event is somewhat different: Only when making the browser popState will be called only when behavior is triggered. It will be triggered when the user clicks the browser's back button and forward button, or uses JavaScript to call the History.back(), History.forward(), and History.go() methods.

Conforms to URL address specifications, no # is required, and it is more beautiful to use

When the user

manually enters the address or refreshes the page, a url request

The compatibility is relatively poor, and the new pushState()
replaceState( are used in the HTML5 History object. ) method requires the support of a specific browser.

What is the difference between $route and $router? $router is an instance object of VueRouter, representing the only router object for the entire application. Contains routing jump methods, hook functions, etc. $route is the current routing object, which represents the routing rules of this component. Each route will have a route object, which is a local object.

Vue-router parameters are passed in several ways, what are the differences?

-DescriptionHow to specify the jump routeIf no parameters are passedCan parameters be passed without the required valueparams parameterparams is part of the route , If placeholders are configured, query parametersquery will not

Vue-router parameter loss problem

When the params parameter is passed, the parameters received by the setting placeholder are passed, and the address bar will not be displayed and Refresh will be lost.

Solution: You can get the parameters and save them locally through this.$route.params

vue-router has several hooks function? What exactly is it and what is the execution process?

vue-router The navigation guard provided is mainly used to guard navigation by jumping or canceling.

Global routing guards: There can be multiple calls based on the order of creation.
- router.beforeEach() Global front guard, will be triggered every time you navigate .
- router.afterEach() Global post route guard, after each route jump is completed. Next function will not be accepted, the jump has been completed and has entered the component
- router.beforResolve() Global parsing guard, before routing jump, all In-component guards and Asynchronous routing components are triggered after being parsed, and they will also be triggered every time they navigate. After the parsing is completed, the navigation is determined and ready to jump.
Route guard within the component
- beforeRouteEnter() is called before the route enters the component. This hook is between beforeEach and beforeEnter After.
  You have not entered the component yet, and the component instance has not been created yet. Therefore, the component instance cannot be obtained. At this time, this is undefined and is triggered before the beforeCreate life cycle.
- beforeRouteUpdate() this is already available, so there is no need to pass a callback to next. For a path /foo/:id with dynamic parameters, when jumping between /foo/1 and /foo/2, since the unified Foo component will be rendered, this component instance will be reused. This hook can be called in this case.
- beforeRouteLeave()Called when leaving the component, this is already available, so there is no need to pass a callback to next.
Exclusive routing guard
- beforeEnter() You need to define the beforeEnter guard on the routing configuration, this The guard is only triggered when entering the route, executed immediately after beforeEach, and will not be triggered when params, query or hash change.

The order of calls before entering the component

beforeEach()=>beforeEnter()=>beforeRouteEnter()=>beforeResolve() This The process cannot use this because the component instance has not been created yet, so you need to use the next function

Complete navigation parsing process 1. Navigation is triggered.
2. Call the
beforeRouteLeave guard in the deactivated component. 3. Call the global
beforeEach guard. 4. Call the
beforeRouteUpdate guard in the reused component. 5. Call
beforeEnter in the routing configuration. 6. Parse asynchronous routing components.
7. Call
beforeRouteEnter in the activated component. 8. Call the global
beforeResolve guard. 9. Navigation is confirmed.
10. Call the global afterEach hook.
11. Trigger DOM update.
12. Call
beforeRouteEnter and pass to the next callback function in the guard. The created component instance will be passed in as a parameter of the callback function.

[Compilation and sharing] Some vue-router related interview questions (with answer analysis)

keep-alive

keep-alive can implement component caching, The current component will not be uninstalled when the component is switched.

keep-aliveThe tag mainly has three attributes: include, exclude, and max

include, exclude The first two attributes allow keep-alive conditional caching
max You can define the maximum number of cached components. If this number is exceeded, Before the next new instance is created, the instance in the cache component that has not been accessed for the longest time will be destroyed.

Two life cycles

activated/deactivated, used to know whether the current component is active.

Keep-alive principle cache management special mount/unmount process

Special uninstall/mount process:

activated/deactivated Cache management:
LRU (Least Recently Used) Least Recently Used is an elimination algorithm

Special uninstall/mount process Since it cannot be The component is truly uninstalled, so keep-alive moves the component from the original container to another fake container to achieve fake uninstallation. When mounting, it is moved from the hidden container to the original container. Corresponding to the component's
activated and deactivated life cycle keepAlive will mark internal components (that need to be cached)

Add the shouldKeepAlive attribute on the vnode object of the internal component to tell the renderer that when the component is unloaded, the component needs to be cached and not actually uninstalled
Add keptAlive on the vnode object of the internal component Attribute, if the component has been cached, add a mark to indicate that the renderer will not be remounted and can be activated directly.

[Compilation and sharing] Some vue-router related interview questions (with answer analysis)

Cache strategy: Recently used at least

Use Map object cache to cache components. The key is the vnode.type value, and the value is the vnode object, because there is a reference to the component instance (vnode.component)

in the vnode object of the component.

cache The former is used to store the virtual dom collection of cache components
keys The latter is used to store the key collection of cache components

Generate a cache key based on the component ID and tag, and check whether the component instance has been cached in the cache object. If it exists, directly retrieve the cached value and update the key's position in keys (updating the key's position is the key to implementing the LRU replacement strategy).
If it does not exist, store the component instance in the map object and save the key value. Then check whether the number of cached instances exceeds the max setting value. If it exceeds the max setting value, delete the most recent one according to the LRU replacement policy. The longest unused instance (that is, the key with index 0).

(Learning video sharing: vuejs introductory tutorial, Basic programming video)


Path/params parameter	`You must use name to specify the route`	If this route has params parameters, but this parameter is not passed during the jump, the jump will fail or the page will have no content.	Placeholders that are not included in the delivery path will not be displayed on the address bar and will be lost upon refresh
Path? key1=val1 & key2=val2....	`1. You can use name to specify the route` 2. You can use path to specify the route	query It is a parameter spliced after the url. It doesn’t matter if it is not available.

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