Previously, we introduced the selector querySelector() in HTML5. Today, we continue to share with you the newly added selector querySelectorAll() in HTML5.
The parameters received by the querySelectorAll() method are also CSS selectors, but all matching elements are returned, while the querySelector() method returns the first matching element.
The querySelectorAll() method returns an instance of NodeList. NodeList is an instance with all properties and methods. Its underlying implementation is equivalent to a snapshot of a set of elements, not a dynamic query for document search. This avoids the performance issues typically caused by using NodeList objects.
As long as the parameters passed to the querySelectorAll() method are valid, this method will return a NodeList object regardless of how many elements are found. If no matching element is found, the NodeList will be empty. Let’s look at a small example to better explain it to you.
HTML code
<p id="all" class="all"> <i>梦龙小站</i> <p class="box"> <em class="span">梦龙小站</em> </p> <i class="span">梦龙小站</i> <p class="box"> <em>梦龙小站</em> </p> </p>
JavaScript code
//获取类名为all的<p>中所有的<i>元素,类似于getElementsByTagName("i") var i = document.getElementById("all").querySelectorAll("i"); //获取类名为span的所有元素 var span = document.querySelectorAll(".span"); //获取所有<p>标签中的所有<em>元素 var em = document.querySelectorAll("p em");
To get each element in the returned NodeList, you can use the item() method or the square bracket syntax. A small example is as follows.
HTML code
<p id="all" class="all"> <i>梦龙小站</i> <p class="box"> <em class="span">梦龙小站</em> </p> <i class="span">梦龙小站</i> <p class="box"> <em>梦龙小站</em> </p> </p>
JavaScript code
//获取所有<p>标签中的所有<em>元素 var em = document.querySelectorAll("p em"); var i, len, emOne; for(i=0, len = em.length; i<len; i++){ emOne = em[i]; //或者 em.item(i); emOne.className = "meng"; }
If a selector that is not supported by the browser is passed in as a parameter to the querySelectorAll() method or there is a syntax error in the selector, the querySelectorAll() method will report an error.
HTML5 actual combat and analysis of CSS selectors - querySelectorAll() is introduced here. The querySelectorAll() method is only a small part of HTML5. On the road to learning HTML5, we digest every little piece of knowledge and move towards the end one step at a time. Thank you for your support to Menglong Station. The actual combat and analysis of HTML5 are still continuing. You are welcome to continue to follow.
The above is the content of HTML5 actual combat and analysis of CSS selector - querySelectorAll(). For more related content, please pay attention to the PHP Chinese website (www.php.cn)!

HTML5 code consists of tags, elements and attributes: 1. The tag defines the content type and is surrounded by angle brackets, such as. 2. Elements are composed of start tags, contents and end tags, such as contents. 3. Attributes define key-value pairs in the start tag, enhance functions, such as. These are the basic units for building web structure.

HTML5 is a key technology for building modern web pages, providing many new elements and features. 1. HTML5 introduces semantic elements such as, , etc., which enhances web page structure and SEO. 2. Support multimedia elements and embed media without plug-ins. 3. Forms enhance new input types and verification properties, simplifying the verification process. 4. Offer offline and local storage functions to improve web page performance and user experience.

Best practices for H5 code include: 1. Use correct DOCTYPE declarations and character encoding; 2. Use semantic tags; 3. Reduce HTTP requests; 4. Use asynchronous loading; 5. Optimize images. These practices can improve the efficiency, maintainability and user experience of web pages.

Web standards and technologies have evolved from HTML4, CSS2 and simple JavaScript to date and have undergone significant developments. 1) HTML5 introduces APIs such as Canvas and WebStorage, which enhances the complexity and interactivity of web applications. 2) CSS3 adds animation and transition functions to make the page more effective. 3) JavaScript improves development efficiency and code readability through modern syntax of Node.js and ES6, such as arrow functions and classes. These changes have promoted the development of performance optimization and best practices of web applications.

H5 is not just the abbreviation of HTML5, it represents a wider modern web development technology ecosystem: 1. H5 includes HTML5, CSS3, JavaScript and related APIs and technologies; 2. It provides a richer, interactive and smooth user experience, and can run seamlessly on multiple devices; 3. Using the H5 technology stack, you can create responsive web pages and complex interactive functions.

H5 and HTML5 refer to the same thing, namely HTML5. HTML5 is the fifth version of HTML, bringing new features such as semantic tags, multimedia support, canvas and graphics, offline storage and local storage, improving the expressiveness and interactivity of web pages.

H5referstoHTML5,apivotaltechnologyinwebdevelopment.1)HTML5introducesnewelementsandAPIsforrich,dynamicwebapplications.2)Itsupportsmultimediawithoutplugins,enhancinguserexperienceacrossdevices.3)SemanticelementsimprovecontentstructureandSEO.4)H5'srespo

The tools and frameworks that need to be mastered in H5 development include Vue.js, React and Webpack. 1.Vue.js is suitable for building user interfaces and supports component development. 2.React optimizes page rendering through virtual DOM, suitable for complex applications. 3.Webpack is used for module packaging and optimize resource loading.


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