<> interview vue Common interview questions and written questions for front end engineers .

Interview nearly a dozen companies, summed up a set VUE Interview questions , Hope to help more people .

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yes MVVM Understanding of

MVVM Divided into Model,View,ViewModel The three .
Model: Representative data model
View: Representative view
ViewModel: Connecting views and models , Realize the bidirectional binding of data

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Vue The principle of data bidirectional binding

Using hijacking data publisher - The way of subscriber mode , adopt Object.defineProperty() To hijack the properties setter,getter, Publish messages to subscribers when data changes , Trigger the corresponding listening callback . When an ordinary
JavaScript Object to Vue As part of it data Option ,Vue Will traverse its properties , use Object.defineProperty Turn them into
getter/setter, Users can't see it getter/setter, But inside, they let me know Vue Tracking dependency , Notifies changes when properties are accessed and modified .
1, Implementation of a data listener Observer, It can monitor all properties of data objects , If there is any change, you can get the latest value and inform the subscriber
2, Implementation of an instruction parser Compile, Scan and parse the instructions of each element node , Replace data according to instruction template , And bind the corresponding update function
3, Implement a Watcher, As a connection Observer and Compile The bridge of , Be able to subscribe and receive notification of each property change , Execute the corresponding callback function of instruction binding , To update the view

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yes webpack Understanding of

Front end packaging tools …

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Understanding of front end Engineering

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On Modularization , Understanding of componentization

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use vue-lic Build a Vue Project for

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yes npm Understanding of

Third party library management tools

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ES6 What new concepts have been put forward

1.var let
2. Arrow function
3. Template string ( backquote )
4. Destructuring assignment
5.import,export
6.class


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HTTP Common status codes

400 Syntax error in client request , Not understood by the server
403 The server received the request but refused to serve |
200 Client request successful |
404 The requested resource does not exist eg: Wrong input URL |
500 An unexpected error occurred on the server |
503 The server is currently unable to process client requests , It may return to normal after a period of time

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Common methods of array , And use

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let ,var ,const The difference between the two

var Declared variables can be declared repeatedly , and let You can't repeat the statement
var Is not limited to the block level , and let Is it limited to the block level
var Meeting with window Phase mapping ( A property will be hung ), and let Not with window Phase mapping
var Variables can be accessed on top of the declaration , and let There is a temporary dead zone , Accessing variables on the top of the declaration will report an error
const Must be assigned after declaration , Otherwise, it will report an error
const Defining immutable quantities , If you change, you will report an error
const and let It won't be the same with you window Phase mapping , Support for block level scopes , Accessing variables on the top of the declaration will report an error

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Cross domain problems How to solve it

jsonp

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How to solve the problem of browser compatibility

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about data security Measures taken

md5, Symmetric encryption , Asymmetric encryption

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Vue Family bucket ——vue,vue-router,vuex

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vuex The five core attributes of

state,getter,mutations,actions,modules

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v-show and v-if The difference between

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Value transfer of parent-child components

The parent component passes the value to the child component :
The first step : In parent component v-bind:parentmsg=“ Of the parent component data value ”(parentmsg This name can be customized )
Step two : In subcomponents props:[‘parentmsg’]
{{parentmsg}} So you can use it The value of the parent component
The parent component passes the method to the child component :
The first step : In the parent component @func= Parent component method name ( Method name without ‘()’,func Customizable )
Step two : Write in subcomponent method this.$emit(‘func’, Method parameters ) (func Customizable , Nonparametric method ‘ Method parameters ’ Don't write it )

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The way of route jump

1.<router-link to='home'> router-link
2. router.push('/home')

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Vue Life cycle of an instance

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vue-router in hash Mode and history The difference between models

The most intuitive difference is in the url in hash I brought one # and history There is no such thing ;
history Back end support required ;
history Refresh or jump back after jump will report an error

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yes ui Use of framework

element-ui,iview,ionic

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angular and vue A comparison of

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Original Ajax How to send a request

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The concept of closure

Function nested function , Internal functions refer to external function variables , After external function call , Its objects should have been destroyed , But closures exist , The variable object that still gives us access to the external function , As a result, the garbage collection mechanism did not take effect , Variables are saved , Memory leak .

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Vue How to send requests in

vue-router

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axios How to send a request

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Front end cache

cookie, WebStorage

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CSS Common layout

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You used it CSS frame

less

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Understanding of unidirectional data flow

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Calculation properties (computed) and watch The difference between

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Callback function

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Promise Three states

pending,fulfilled,rejected( up in the air , perform , refuse ), There can only be one state at a time , And once the state changes, it can't change again .promise Is a constructor ,promise Object represents an item with two possible results ( Success or failure ) The task of , It also holds multiple callbacks , When different results appear, corresponding callbacks are issued respectively .
1. initialization , state :pending
2. When calling resolve( success ), state :pengding=>fulfilled
3. When calling reject( fail ), state :pending=>rejected

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Concepts of synchronization and asynchrony

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Get Requests and Post The difference between requests

* Get It's not safe , Because in the transmission process , The data is placed in the requested URL in ;Post All operations of are invisible to the user .
2 Get The amount of data transferred is small , This is mainly due to URL Length limit ;Post A large amount of data is transmitted , Generally, it is not limited by default .
3.Get limit Form The value of the dataset for the form must be ASCII character ; and Post Support the whole ISO10646 character set .
4. Get However, the efficiency of implementation is higher than that of control Post Good method .Get yes form Default method for submission .
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Custom filter

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How to use native js Bind multiple buttons to a button onclick event

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VUE If you register global components

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list css Selector and priority

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Weight calculation rules

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This paper expounds several ways of clearing floating and their advantages and disadvantages

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sketch cookies sessionStorage and localStorage difference

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Array de duplication

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mvvm,mvc Principle and difference

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