Event handling mechanism

The JavaScript event handling mechanism is the core of browser-user interaction. When a user interacts with a page, an event object is generated and propagated through the event flow, which includes the capture phase, target phase, and bubbling phase. Developers can listen for events in various ways, including HTML attributes, DOM properties, and the `addEventListener` method. The event object contains rich information, such as coordinates and the triggering element. Event delegation leverages the bubbling mechanism to handle child element events on a parent element. Custom events can also be created. Methods of the event object can prevent default behavior or stop propagation. High-frequency events require throttling to optimize performance. Improper event binding may lead to memory leaks. Mobile devices have unique touch events. Keyboard events can handle key combinations. Forms have specific events like submit and input. The Drag and Drop API enables drag-and-drop functionality. Page lifecycle events handle DOM loading, resource loading, etc. Animation frame events optimize animation performance. Global error handling captures uncaught exceptions. Clipboard events manage copy-paste operations.

DOM style manipulation

DOM style manipulation is a crucial technique in front-end development for dynamically modifying element styles. Through JavaScript, developers can manipulate inline styles, class names, and stylesheets to achieve rich interactive effects. Inline styles are modified directly via the element's `style` attribute, which has the highest priority. Class name manipulation uses `classList` to efficiently manage multiple style classes. `getComputedStyle` retrieves the final applied styles of an element, including inherited styles. Stylesheet operations allow global modifications to CSS rules. Combining CSS variables with JavaScript enables flexible animation control. Frequent style modifications require performance optimizations, such as batch operations and using `requestAnimationFrame`. Responsive design dynamically adjusts styles based on window size. Pseudo-elements are indirectly controlled via CSS variables. Practical applications include drag-and-drop components and modal dialogs. Browser compatibility requires handling prefix differences. Modern frameworks encapsulate style manipulation, but understanding the underlying principles remains important. React and Vue provide declarative style-binding mechanisms.

DOM attribute manipulation

DOM attribute manipulation is a core part of JavaScript's interaction with web elements, providing various methods to access and modify attributes. These include dot notation and square bracket notation for standard HTML attributes, as well as universal APIs like `getAttribute` and `setAttribute` for handling arbitrary attributes. Boolean attributes require special handling. HTML5's `dataset` property simplifies working with custom data attributes. Style manipulation can be done via the `style` property or `getComputedStyle`, while `classList` is more suitable for fine-grained class control than `className`. Note the distinction between HTML attributes and DOM properties. Frequent attribute operations may impact performance. Form controls and ARIA attributes have specific handling methods. Attribute changes can be monitored using `MutationObserver`. Pay attention to naming conventions for attribute conversion, and consider browser compatibility and attribute manipulation within Shadow DOM.

DOM node operations

DOM node manipulation is one of the core skills in front-end development. The DOM represents a document as a node tree, including document nodes, element nodes, text nodes, attribute nodes, and comment nodes. Common node query methods include querying by ID, class name, tag name, and CSS selector. Creating nodes involves element nodes, text nodes, and attribute nodes. Adding nodes can be done through appending, inserting, or replacing. Modifying node content involves changes to text, HTML, and styles. Node deletion operations include removing nodes and clearing content. Node traversal involves parent-child and sibling relationships. Advanced operations include cloning nodes, using document fragments, and custom data attributes. Performance optimization recommendations include batch operations, offline operations, caching query results, and using event delegation. Practical application examples include dynamic list manipulation and form dynamic validation. Modern DOM manipulation APIs include classList and MutationObserver. Cross-browser compatibility requires attention to differences between textContent and innerText, event handling discrepancies, and classList compatibility.

DOM query methods

DOM querying is the fundamental method for JavaScript to manipulate webpage elements. Browsers provide various native APIs for element positioning: `document.getElementById` retrieves a single node by ID with the fastest speed, `getElementsByClassName` and `getElementsByTagName` return dynamic HTMLCollections, while `querySelector` and `querySelectorAll` support CSS selector syntax and return static NodeLists. The document offers special collections for quick access to common elements like links and forms. Node relationship queries allow relative positioning from existing nodes. Attribute selectors support exact and fuzzy matching. Form elements have dedicated query methods. Performance optimization recommendations include caching query results and narrowing the query scope. Dynamic filtering techniques combine array methods to process query results. `MutationObserver` can monitor DOM changes. Compatibility solutions address issues in older browsers. Complex selectors demonstrate the powerful functionality of CSS3. Custom data attributes and Shadow DOM queries meet modern development needs. Strategies for handling dynamically loaded content include event delegation and waiting for elements. Different selectors exhibit performance variations. Error handling mechanisms enhance code robustness.

Node types and attributes

In JavaScript, DOM nodes are the fundamental units of a document's structure and include various types, each corresponding to a specific numeric constant. Element nodes, the most common type, represent HTML tags and have attributes and child nodes. Text nodes contain textual content, while attribute nodes represent element attributes. Comment nodes store comment content. The document node represents the entire document and serves as the root of the DOM tree. Document fragment nodes are used for efficiently manipulating multiple nodes. All nodes share basic properties and methods, such as node name, type, value, and relationships with parent, child, and sibling nodes. DOM operations include creating, adding, cloning, inserting, replacing, and removing nodes. Modern DOM provides more concise methods like `querySelector` and `classList`, and allows the creation of custom element nodes. By understanding these node types and properties, one can effectively manipulate and manage the DOM structure.

The DOM tree structure

The DOM tree is a tree-like representation of an HTML document in memory, composed of various types of nodes, including document nodes, element nodes, attribute nodes, text nodes, and comment nodes. The article elaborates on methods for traversing the DOM tree, such as parent-child traversal, sibling traversal, and using the `querySelector` method, as well as DOM tree modification operations like creating, adding, and deleting nodes. It also introduces performance optimization techniques for the DOM tree, including using document fragments, batch style updates, and event delegation. Additionally, the article covers the concept of the virtual DOM, DOM tree access control such as the same-origin policy and Shadow DOM, along with debugging techniques and compatibility issues. Finally, it mentions modern DOM APIs like `MutationObserver`. These contents provide comprehensive guidance for understanding and manipulating the DOM tree.

Array-like object

Array-like objects in JavaScript are structures that resemble arrays but are not true arrays, possessing numeric indices and a length property but lacking native array methods. Common examples include the `arguments` object in functions, `NodeList` from DOM operations, and strings. Array-like objects can be converted to real arrays using `Array.from`, the spread operator, or `Array.prototype.slice.call`. They can also be custom-implemented, but limitations exist, such as the inability to directly call array methods. In practice, array methods can be borrowed or the `length` property can be checked to manipulate and identify array-like objects.

Type conversion and detection

JavaScript type conversion is divided into implicit and explicit methods. Implicit conversion is automatically performed by the engine, commonly seen in operator operations and comparisons. Explicit conversion is achieved through specific methods like `String()` and `Number()`. Type detection can be done using methods such as `typeof` and `instanceof`. Object-to-primitive conversion involves `valueOf` and `toString` methods. Date objects and JSON also have special conversion rules. Best practices include avoiding pitfalls of implicit conversion, handling edge cases, and customizing type conversion. Understanding these mechanisms helps in writing more reliable code.

Flow control statements

JavaScript control flow statements include conditional statements, loop statements, and jump statements. Conditional statements include `if-else` and `switch`, which are used to execute different code blocks based on different conditions. `if-else` executes code by evaluating conditions, while `switch` matches the expression value to `case` for execution. Loop statements include `for`, `while`, `do-while`, `for-of`, and `for-in`, which are used to repeatedly execute code. `for` is suitable for known loop counts, `while` loops while the condition is true, `do-while` executes at least once, `for-of` iterates over iterable objects, and `for-in` traverses object properties. Jump statements include `break`, `continue`, and `return`: `break` exits a loop or `switch`, `continue` skips the current iteration, and `return` returns a function value. Exception handling uses `try-catch-finally`. Label statements work with `break` and `continue`. The ternary operator is a shorthand form of `if-else`.