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A summary of the use of Ant-Design and common components and their basic usage?
Ant-design provides components for React, Angular, and Vue, as well as common base components for PCS and mobile devices. The demo provided by Ant-Design is very rich and has a style that basically covers development requirements. Antd Demo is written by many people, so you can see that there are different styles of implementation, which can well meet different development styles.
Common components include: Button, Form, Radio, Select, TimePicker, Upload, Table, etc. When using it, you need to refer to Demo to write, and at the end of the component interface page, there are properties and notes. Can be very convenient to achieve the effect.
2. What character entities are commonly used in the front end and how to write them?
Because reserved characters exist, character entities can be used when they need to be displayed. Common character fonts are:
(1) blank & NBSP; (2) less than sign < (3) double quotation marks “; (4) Single quotation marks ‘ (5) & and symbol & (6) > > >;
3. React lifecycle and what does different lifecycle mean?
1) Initialize state from constructor. 2) componentDidMount for asynchronous loading data, add event listener. 3) getDerivedStateFromProps updates the props passed to state. 4) componentDidUpdate handles requests triggered by state changes.
4. What are the commonly used chart drawing tools and what functions can they achieve?
EChats provides multi-dimensional data display on different platforms and supports multiple visualization types on multiple devices, such as line charts, bar charts, scatter charts, pie charts, and K-charts.
5. What is the process of uploading OSS files in Ali Cloud?
Because of the key retention issues involved in OSS, it is best to send images to the backend, which then uplows the images to OSS and returns the OSS URL. The image selection uses the Upload component of Ant-Design.
6. What are the main functions of Redux and how to use it?
The main function is to centralize all the states at the top of the component, allowing for flexible distribution of all states to all components.
Store: A place where data is stored. The entire app has a Store. State: Contains all data. One state corresponds to one view. As long as the state is the same, the view is the same. Action: Notifies the View action to change the state, thus changing the View. The only way to change state is to use Action.
7. How to operate the third-party library that the upgrade project relies on?
Using NPM outdated, you can check the latest version of the package in NPM, then use NCU-u to upgrade the dependent library, and finally use NPM install to install the new version.
Ncu is a tool for nom-check-updated, which is installed via NPM install -g npm-check-updates. After the upgrade is complete, you need to check whether the version of the dependent third-party library has been upgraded to a major version, for example, upgrade from 1.x to 2.x or upgrade from 3.x to 4.x. If cross-version upgrade is involved, be careful. You need to check the corresponding official version migration record to upgrade the code.
Therefore, it is generally recommended to periodically upgrade the version of the third-party library, which can effectively fix the bugs of the third-party inventory and avoid the large impact of the upgrade caused by the large version.
8. How to use Hook in react?
You can use state and other React features without writing a class. Declare new variables using useState
Const [count, setCount] = useState(0); // Declare a new state variable called "count" const [count, setCount] = useState(0);Copy the codeUseEffect adds the ability to manipulate side effects to function components for the same purpose as componentDidMount, componentDidUpdate, and componentWillUnmount. React calls the side effects function after every render (including the first one).
ComponentDidMount and componentDidUpdate: Document. title = 'You clicked ${count} times'; useEffect() => {document.title =' You clicked ${count} times'; });Copy the codeUseEffect can be used multiple times within components.
useEffect(() => {
ChatAPI.subscribeToFriendStatus(props.friend.id, handleStatusChange);
return () => {
ChatAPI.unsubscribeFromFriendStatus(props.friend.id, handleStatusChange);
};
});
Copy the codeSide effects functions can also specify how to “clear” side effects by returning a function. For example, in the above component, the side effects function is used to subscribe to a friend’s online status and to clear it by unsubscribing. Can be understood as before is added in the componentDidMount ChatAPI. SubscribeToFriendStatus (props. Friend. Id, handleStatusChange); To subscribe to a friend online, and then added in componentWillUnmount ChatAPI. UnsubscribeFromFriendStatus (props. Friend. Id, handleStatusChange); To unsubscribe.
UseEffect the second argument is an array of dependent values. Effect is rendered only when the array values change. If an empty array is passed in, it is executed only once when the component is mounted and unmounted.
What is the meaning of rebase and fast forward in Git?
The biggest difference between Git and SVN is distribution, which means that after checking out the project, you can submit the code locally, view the historical version, create a new branch of the project, etc.
Git uses rebase to manage branches to avoid disjointing branches caused by merging multiple branches. In A merger, when the branch line A to be merged and the branch B to be merged, A’s base point is that B has no new commit on B, then fast forward and A merger commit is not generated. Fast forward can also be turned off to add a merge commit, which makes it easy to see who has done a merge.
10, CSS selector list priority and weight?
1. General selector (*) 2. Element (type) selector weight 1 3. Attribute selector 5. Pseudo-class 6.ID selector weight 100 7. Inline style weight 1000! The important rule overrides any other declarations and is only used on substitute pages that need to overwrite the entire site or external CSS.
11. What are the common attributes of the CSS configuration and their functions?
| classification | attribute | value |
|---|---|---|
| Width and height | Width the width; Height is high; Max-height follows the parent tag | |
| Font properties | Color color; The font-family font; Font-size Text size; Font-weight Indicates the weight of the text | Normal Default value Bold Bolder Lighter 100 to 900 Parameter Description Value Inherit Font size of class elements |
| color | Hex value: #FF0000; Words: blue, red; RGB value: (255, 0, 0); Rgba (200, 0, 0, 0.3) | |
| Text attributes | Text-align, text-decoration, text-indent | Left justify right justify center justify both ends; None default underline overline overline line-through Through text inherit parent class properties |
| Background properties | Background-color: red; Background-image: url(‘1.jpg’); Background-repeat: repeat; Background position Background-position: Right top | |
| CSS box | Margin controls the distance between elements; Padding controls the distance between the content and the border; Border The inside margin and the border around the content; Content displays text and images. | Order of abbreviations: top right bottom left |
| A border | border-width, border-style, border-color; Border :2px solid red; | Border-radius implements rounded border; The bounding bounding bounding bounding bounding bounding bounding bounding bounding bounding bounding bounding bounding bounding bounding bounding bounding bounding bounding bounding bounding bounding bounding bounding bounding bounding bounding bounding edge |
| According to | display | None is not displayed; Block covers the entire page width; Inline displays as inline elements; Inline-blocks have inner elements and block-level elements |
| floating | Float Any element can float; The clear property specifies that no other floating elements are allowed on the side; | Properties of float: left left, right right, none does not float. The clear attribute left does not float elements on the left, right does not float elements on the right, both does not float elements on the left, and none does not float elements on the right. Inherit the parent element; |
| The overflow | overflow | Visible content is unclipped, hidden content is clipped and the rest of the content is invisible, Scroll content is clipped and shows the scroll bar to view the rest of the content, Auto content is clipped and shows the scroll bar to view the rest of the content, inherit from the parent element |
| positioning | position | A. static B. relative C. absolute D. fixed |
12. The function of BwebPack and how to use it?
Module packing, analyzing the project structure, finding JavaScript modules and extension languages (Scss, TypeScript, etc.) that browsers don’t run directly, and packaging them into appropriate formats for use by browsers. Use CSS-loader and style-loader to embed stylesheet tables into webpack packed JS files.
CSS preprocessors using less-loader, Sas-Loader, or stylus-loader can convert special types of statements into CSS statements that can be recognized by the browser.
Webpack uses plug-ins to extend WebPack functionality and implement and perform related tasks throughout the build process. For example, HtmlWebpackPlugin, based on a simple template to generate the final Html5 file and automatically reference the packaged JS file in the file.
13, Promise implementation and advantages and disadvantages
Promise is used to indicate the final completion (or failure) of an asynchronous operation and its resulting value.
Var myPromise = new Promise(resolve, reject) => { If (resolve(value)} else if (reject(error)) {reject(error)}}) myPromise.then((value) => {if (value) {reject(error)}}) myPromise.then(value) => { Use value}, (error) => {// call after failure, error})Copy the codeAdvantages: Eliminates callback hell, makes asynchronous task writing more standardized and concise.
Cons: You can’t cancel a Promise. Once you create a Promise, it executes immediately. Second, if you don’t set a callback function, the Promise throws an error internally and doesn’t react externally.
Third, when in a pending state, there is no way to know what stage of progress is currently being made.
14. Http status code and its meaning
2xx: the request succeeds. 3xx: The resource is redirected to another URL. 4xx: the client error, the request syntax is incorrect, or the corresponding resource is not found. Resources (web pages, etc.) are permanently transferred to another URL. The return value contains the new URL, and the browser automatically directs to the new URL 302: temporary transfer. The client should access the original URL 304: Not Modified. 404: Requested resource (web page, etc.) does not exist. 500: Internal server error
15. Use of async and await
Async /await is a new way to write asynchronous code. Previous methods have callback functions and promises. Async /await is implemented based on promises and cannot be used for normal callback functions. Async /await, like Promise, is non-blocking. Async /await makes asynchronous code look like synchronous code, which is part of its magic.
16, setTimeout time delay why not
Single thread, execute synchronous main thread first, then execute asynchronous task queue.
17, let const var scope and difference
Block-level scope, temporary dead zone. Var defines variables that can be accessed across block scopes, not function scopes.
Variables defined by lets can only be accessed in the block scope, not across the block scope or function scope.
Const defines a constant, which must be assigned when created, can only be accessed in the block scope and cannot be modified.
18, For in, forEach and for of
For in groups iterate over properties and methods on array prototypes, and are better suited for traversing objects. If you don’t want to iterate through the prototype methods and properties of myObject, you can check the hasOwnProperty method inside the loop to see if a property is an instance property of the object.
ForEach does not support break, continue, or return
For of can successfully iterate over a set of values, rather than indexes, without iterating through stereotypes.
19, localStorage and sessionStorage and cookie difference summary
Common: They are saved in the browser and belong to the same source.
LocalStorage and sessionStorage are collectively called Webstorages. They are stored in browsers and do not participate in server communication. The size is 5M.
Different life cycles: localStorage permanent storage, sessionStorage current session. Can be manually deleted.
Different scopes: Different browsers do not share local and session, and different sessions do not share sessions.
Cookie: the set expiration time is valid until the size of 4K. There is a limit to the number, which varies with the browser. Generally, the number is 20. Carried in HTTP headers, too many can cause performance problems. Can own package, also can use native.
20. Life cycle of wechat applets?
OnLoad page loading: A page is called only once, and you can get the query parameter in onLoad to open the current page.
The onShow page displays: it is called every time the page is opened.
OnReady page is rendered for the first time: a page is called only once, indicating that the page is ready to interact with the view layer.
OnHide page hide: called when navigateTo or bottom TAB is switched.
OnUnload page unload: Performed when a page is destroyed.
Micro channel small program principle?
Wechat applet is developed by JavaScript, WXML and WXSS.
JavaScript: First of all, JavaScript code is run in wechat App, not in browser. Therefore, some H5 technology applications need wechat App to provide corresponding API support, which limits the application of H5 technology and cannot be called strict H5. Similarly, wechat provides some unique apis that H5 does not support or are not particularly well supported.
WXML: WXML wechat is developed based on XML syntax, so you can only use the existing tags provided by wechat during development. HTML tags are not available.
WXSS: Has most of the features of CSS, but not all of them, and there is no detailed documentation of what is and isn’t supported. The architecture of wechat is data-driven. UI and data are separated, and all page updates need to be realized through changes to data. Wechat program is divided into two parts: WebView and appService. Among them, WebView is mainly used to show UI, and appService is used to deal with business logic, data and interface calls. They run in two processes, through the system layer JSBridge to achieve communication, UI rendering, event processing.
22. HTTP status code and its meaning
| Status code Type Status code | category | The reason the phrase |
|---|---|---|
| 1XX | Information (Informational status code) | The received request is being processed |
| 2XX | Success (Success Status code) | The request is successfully processed |
| 3XX | Redirection (Redirection status code) | Additional action is required to complete the request |
| 4XX | Client Error (Client Error status code) | The server cannot process the request |
| 5XX | Server Error (Server Error status code) | The server failed to process the request |
| 204 | The server processed successfully, but did not return content. | |
| 304 | Not Modified. | The requested resource is not modified, and the server does not return any resources when it returns this status code. Clients typically cache accessed resources by providing a header indicating that the client wants to return only resources that have been modified after a specified date |
| 400 | Bad Request | Client request syntax error, server cannot understand |
| 403 | Forbidden | The server understands the request from the requesting client, but refuses to execute the request |
| 404 | Not Found | The server could not find the resource (web page) based on the client’s request. |
With this code, a web designer can set up a personalized page that says “the resource you requested could not be found.
1. Ajax implementation principle and method? 2. How does key work in VUE? 3. What is the principle of VUE bidirectional binding? What is the function of $nextTick in VUE? 5, talk about front-end engineering, modular, componentization? Vue, JQ, React, Angular, vue, JQ, React, Angular Where to store the event loop Sort [3, 15, 8, 29, 102, 22] by sort() React life cycles are triggered by changes in data. What is elastic layout? 19. Write responses? 20. Common browser compatibility issues? What’s new in C3:23. What is typescript 24? 26. What is modular programming? 27. Performance optimization? 28. What is HTTP protocol: ■ Audio and video elements will be automatically played in ios and Android. ■ Make text uncopy-able. ■ Horizontal and vertical center An object is an array type. CORS HTTP request is an array type. 38, What is the difference between SRC and href? What is a CSS HACK? Elegant degradation and progressive enhancement? Implementation of the new operator 42. Recursive deep copy 43. Four common JS memory leaks
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