Always display Div code in the middle of the screen (css js)_javascript tips

The scope of JavaScript determines the accessibility scope of variables, which are divided into global, function and block-level scope; the context determines the direction of this and depends on the function call method. 1. Scopes include global scope (accessible anywhere), function scope (only valid within the function), and block-level scope (let and const are valid within {}). 2. The execution context contains the variable object, scope chain and the values of this. This points to global or undefined in the ordinary function, the method call points to the call object, the constructor points to the new object, and can also be explicitly specified by call/apply/bind. 3. Closure refers to functions accessing and remembering external scope variables. They are often used for encapsulation and cache, but may cause

There is an essential difference between JavaScript's WebWorkers and JavaThreads in concurrent processing. 1. JavaScript adopts a single-thread model. WebWorkers is an independent thread provided by the browser. It is suitable for performing time-consuming tasks that do not block the UI, but cannot operate the DOM; 2. Java supports real multithreading from the language level, created through the Thread class, suitable for complex concurrent logic and server-side processing; 3. WebWorkers use postMessage() to communicate with the main thread, which is highly secure and isolated; Java threads can share memory, so synchronization issues need to be paid attention to; 4. WebWorkers are more suitable for front-end parallel computing, such as image processing, and

CompositionAPI in Vue3 is more suitable for complex logic and type derivation, and OptionsAPI is suitable for simple scenarios and beginners; 1. OptionsAPI organizes code according to options such as data and methods, and has clear structure but complex components are fragmented; 2. CompositionAPI uses setup to concentrate related logic, which is conducive to maintenance and reuse; 3. CompositionAPI realizes conflict-free and parameterizable logical reuse through composable functions, which is better than mixin; 4. CompositionAPI has better support for TypeScript and more accurate type derivation; 5. There is no significant difference in the performance and packaging volume of the two; 6.

Initialize the project and create package.json; 2. Create an entry script index.js with shebang; 3. Register commands through bin fields in package.json; 4. Use yargs and other libraries to parse command line parameters; 5. Use npmlink local test; 6. Add help, version and options to enhance the experience; 7. Optionally publish through npmpublish; 8. Optionally achieve automatic completion with yargs; finally create practical CLI tools through reasonable structure and user experience design, complete automation tasks or distribute widgets, and end with complete sentences.

Use document.createElement() to create new elements; 2. Customize elements through textContent, classList, setAttribute and other methods; 3. Use appendChild() or more flexible append() methods to add elements to the DOM; 4. Optionally use insertBefore(), before() and other methods to control the insertion position; the complete process is to create → customize → add, and you can dynamically update the page content.

TypeScript's advanced condition types implement logical judgment between types through TextendsU?X:Y syntax. Its core capabilities are reflected in the distributed condition types, infer type inference and the construction of complex type tools. 1. The conditional type is distributed in the bare type parameters and can automatically split the joint type, such as ToArray to obtain string[]|number[]. 2. Use distribution to build filtering and extraction tools: Exclude excludes types through TextendsU?never:T, Extract extracts commonalities through TextendsU?T:Never, and NonNullable filters null/undefined. 3

Microfrontendssolvescalingchallengesinlargeteamsbyenablingindependentdevelopmentanddeployment.1)Chooseanintegrationstrategy:useModuleFederationinWebpack5forruntimeloadingandtrueindependence,build-timeintegrationforsimplesetups,oriframes/webcomponents

varisfunction-scoped,canbereassigned,hoistedwithundefined,andattachedtotheglobalwindowobject;2.letandconstareblock-scoped,withletallowingreassignmentandconstnotallowingit,thoughconstobjectscanhavemutableproperties;3.letandconstarehoistedbutnotinitial