Top new Element Features of html5

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HTML5 Now is not SGMLa subset of the increase was mainly about the image, location, storage, multi-tasking and other features

Painting canvas for media playback videoand audioelements of local offline storage localStoragefor long term storage of data, the browser is closed after data is not lost sessionStoragedata is automatically deleted when the browser is closed meaning of better content elements of language, such as article, footer, header, nav, section form controls, calendar, date, time, email, url, search new technologies webworker, websocket,Geolocation

Elements:

Pure performance basefontelements: big, center, font, s, strike, tt, , u produce a negative impact on the availability of frameelements: frameset, ,noframes

Support for HTML5new tags:

IE8/IE7/IE6 supports document.createElementtags generated by methods. This feature can be used to make these browsers support HTML5 new tags. After the browser supports new tags, you also need to add the default style of the tags.

Of course, you can also directly use mature frameworks, such as html5 shim

< ! - [ if  lt  IE  9 ] >
 
< script > src="http://html5shim.googlecode.com/svn/trunk/html5.js" < / script >
 
< ! [ endif ] - >

What are the html5 new features

HTML5 introduces a number of new elements and attributes that can help you in building modern websites. Here is a set of some of the most prominent features introduced in HTML5.

  • New Semantic Elements − These are like <header>, <footer>, and <section>.
  • Forms 2.0 − Improvements to HTML web forms where new attributes have been introduced for <input> tag.
  • Persistent Local Storage − To achieve without resorting to third-party plugins.
  • WebSocket − A next-generation bidirectional communication technology for web applications.
  • Server-Sent Events − HTML5 introduces events which flow from web server to the web browsers and they are called Server-Sent Events (SSE).
  • Canvas − This supports a two-dimensional drawing surface that you can program with JavaScript.
  • Audio & Video − You can embed audio or video on your webpages without resorting to third-party plugins.
  • Geolocation − Now visitors can choose to share their physical location with your web application.
  • Microdata − This lets you create your own vocabularies beyond HTML5 and extend your web pages with custom semantics.
  • Drag and drop − Drag and drop the items from one location to another location on the same webpage.

Which SEOs should the front-end pay attention to?

  • Reasonable title, , description: keywordsSearch right in front of the three-by-weight decreases, titlethe value of the focus to emphasize the important keywords appear no more than 2 times, and the former rely on different pages titleto be different; descriptionthe high-level summary page content, length Appropriate, do not pile up keywords too much, different pages descriptionare different; just keywordslist important keywords
  • Semantic HTMLcode, in line with W3C specifications: Semantic code makes it easy for search engines to understand web pages
  • Important content HTMLcode is placed first: the search engine crawling HTMLorder is from top to bottom, and some search engines have restrictions on the crawl length to ensure that important content will be crawled
  • Do not use jsoutput for important content : crawlers will not execute js to obtain content
  • Use less iframe: search engines will not crawl iframethe content
  • Non-decorative pictures must be addedalt
  • Improve website speed: website speed is an important indicator of search engine ranking

Steps to enter the URL from the browser address bar to the displayed page

Brief answer

  • According browser requests URL to the DNS DNS to find real IP, initiates a request to a server;
  • The server returns the data after the background processing is completed, and the browser receives the file ( HTML、JS、CSS, image, etc.);
  • The browser parses the loaded resources (HTML, JS, CSS, etc.), and establishes the corresponding internal data structure (such as HTML DOM);
  • Load the parsed resource file, render the page, and finish.

Detailed answer

  1. Received from the browser url to start the network request thread (this part can expand the mechanism of the browser and the relationship between the process and the thread)
  2. Start the network thread to issue a complete HTTP request (this part involves dns query, TCP/IP request, five-layer Internet protocol stack, etc.)
  3. From the server receiving the request to the corresponding background receiving the request (this part may involve load balancing, security interception and internal processing in the background, etc.)
  4. The HTTP interaction between the background and the foreground (this part includes knowledge of the HTTP header, response code, message structure, cookie etc., which can improve the cookie optimization of static resources , as well as encoding and decoding, such as gzip compression, etc.)
  5. Carry out a separate cache problem, HTTP a cache (Cache This section includes http header ETag, catch-control etc.)
  6. Browser receives the HTTP resolution process (after parsing a packet html– lexical analysis and then parsed into doma tree, parsing css generation css, combined into render the tree, and then layout、paintingrendering the synthesized composite layer, GPU process drawing, outside the chain of resources, loaded and DOM Content Loaded the like)
  7. CSS Visual format model (elements rendering rules, such as including blocks, control boxes,, BFC and IFC other concepts)
  8. JSEngine analysis process ( JS interpretation phase, preprocessing phase, execution phase to generate execution context VO, scope chain, recycling mechanism, etc.)
  9. Other (different knowledge modules can be expanded, such as, web, hybrid mode and much more)

How to optimize website performance

  • content aspect Reduce HTTP requests: merge files, CSS sprites sprites, inline Image reduce DNS queries: DNScache, distribute resources to the appropriate number of hostnames, reduce the DOM number of elements
  • Cookie aspectReduce cookie size
  • Server aspect Use CDN configuration ETag to use Gzip Compression compression on components
  • aspect Optimize the picture: According to the actual color needs to select the color depth, compress the optimization css wizard, do not HTML stretch the picture in the middle
  • css aspect Put the style sheet at the top of the page Do not use CSS expressions Use or <link>not@import
  • js aspect The bottom of the script into the page javascript and css the introduction of pressurized from the outside javascript and the css script removes unwanted reduce DOMaccess

Semantic understanding

  • Simply put: do the right thing with the right label!
  • HTML Semantic is to structure the content of the page to facilitate the analysis of browsers and search engines;
  • It CSSis also displayed in a document format without a style and is easy to read.
  • Search engine crawlers rely on tags to determine the context and the weight of each keyword, which is beneficial SEO.
  • Make it easier for people who read the source code to divide the website into blocks, which is convenient for reading, maintaining and understanding

Please describe the difference between cookies, sessionStorage and localStorage?

  • cookieIt is the data (usually encrypted) stored on the user’s local terminal (Client Side) by the website in order to identify the user
  • cookieThe data is always carried in the same http request (even if it is not needed), that is, it will be passed back and forth between the browser and the server
  • sessionStorageAnd localStoragewill not automatically send the data to the server, only save it locally
  • Storage size:cookieThe data size cannot exceed 4k sessionStorageand localStoragealthough there is also a storage size limit, the ratio is cookiemuch larger and can reach 5M or more
  • Duration:localStorageTo store persistent data, the browser is closed after data is not lost unless the initiative to remove data sessionStoragedata is automatically deleted after the window closes the current browser cookiesettings cookieremain in effect until the expiration time, or even if the browser window is closed

Restrictions on page access cookies

cookie (data stored on the user’s local terminal)

Cookies refer to data stored on the user’s local terminal by certain websites in order to identify the user’s identity and perform session tracking. Cookies are almost everywhere in the network system. When we browse the websites we have visited before, the webpage may appear: Hello XXX.

1. Cross-domain issues:

cookieAllow web developers to keep their users’ login status. However, problems can arise when your site has more than one domain name. According to the cookiespecification, one cookiecan only be used for one domain name and cannot be sent to other domain names. Therefore , if one is set for a domain name in the browser cookie, this cookiewill be invalid for other domain names.

solve:

  • Reverse proxy through nginx
  • jsonp request

2. HTTP only is set:

If the HttpOnlyattribute is set in the cookie, the cookieinformation will not be read through the program (JS script, Applet, etc.) , which can effectively prevent XSSattacks.

The role and drawbacks of cookies

The role of cookies

  • The user data can be saved on the client, which plays a simple role in caching and user identification.
  • Save the user’s login status, and the user logs in. After successfully logging in, the server generates a specific cookie and returns it to the client. Next time the client visits any page under the domain name, it sends the cookie information to the server . Determine whether the user is logged in.
  • Record user behavior.

cookie drawbacks

  • To increase traffic consumption, you need to bring cookie information with each request.
  • For security risks, cookies are transmitted in clear text. If the cookie is intercepted by someone, that person can get all the session information.
  • Limits on the number and length of cookies. Each domain can only have 20 cookies at most, and each cookie cannot exceed 4KB in length, otherwise it will be truncated

What is the difference between xhtml and html?

  • Functional differenceMainly XHTML is compatible with major browsers, mobile phones and PDAs, and the browser can also compile web pages quickly and correctly
  • Differences in writing habitsXHTML elements must be properly nested, closed, case sensitive, and the document must have a root element

What are the disadvantages of iframe?

  • iframe will block the main page Onloadevent
  • The retrieval program of the search engine cannot interpret this page, which is not conducive to SEO – iframesharing the connection pool with the main page, and the browser has restrictions on the connection of the same domain, so it will affect the parallel loading of the page
  • iframeThese two disadvantages need to be considered before use . If you need to use it iframe, it is best to javascriptdynamically add srcattribute values to the iframe , which can bypass the above two problems

What does the webpage verification code do and what security issues are it to solve?

  • A public fully automatic program that distinguishes whether the user is a computer or a human. Can prevent malicious password cracking, ticket swiping, and forum irrigation
  • Effectively prevent hackers from continuously attempting to log in to a specific registered user using specific programs to brute force

What is the difference between title and h1, b and strong, i and em?

  • titleThe attribute has no clear meaning and only means that it is a title, H1which means a title with a clear level, which also has a great influence on the crawling of page information;
  • strongKey content is marked with the tone strengthen meaning when read using a reading device network, <strong>it will be re-read, and <B>is showing emphasize content.
  • i The content is displayed in italics, emindicating emphasized text;
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