Share the simplest JavaScript countdown code (complete code attached)

Master basic but in-depth command line skills: proficient in using Tab completion, history, Ctrl R search, pwd positioning and ls-la to view hidden files; 2. Efficiently use Node.js and package manager: make good use of npminit-y, --save-dev, npx without installation and operation, npmrun scripts and outdated inspection, and optimize pnpm speed up; 3. Accurate search code and log: combine grep-r/-i, find files, jq formatted JSON and xargs to find JS files with specific content; 4. Write simple script automation tasks: such as deploy.sh one-click deployment, chmod x grant execution rights; 5. Custom Sh

To determine whether the variable is an array type, the Array.isArray() method is preferred, and secondly, Object.prototype.toString.call() can be used. 1.Array.isArray(variable) returns true or false, suitable for modern browsers and Node.js; 2.Object.prototype.toString.call(variable)==='[objectArray]', compatible with old environments. Avoid using typeof and instanceof because they have flaws in judging arrays. Choose the right method according to your needs: Priority is given if there is no need to be compatible with old versions

Keep dependency version consistent, update dependencies regularly, distinguish dependencies types, and use Monorepo to manage multi-project dependencies. 1. Use package-lock.json or yarn.lock to submit to Git to ensure environmental consistency; 2. Check the dependency tree regularly to avoid duplicate installation and conflicts; 3. Use npmoutdated or yarnoutdated to check for updates, prioritize security issues and evaluate the impact of major version upgrades; 4. Clearly distinguish dependencies and devDependencies to avoid misinstalling development tools in the production environment; 5. Use tools such as Lerna or Nx to uniformly manage shared dependencies and code of multiple projects to improve collaboration efficiency.

Use Jest's MockFunctions and Timers to control asynchronous behavior, and improve testing efficiency through jest.fn() and jest.useFakeTimers(); 2. Use Fixtures and PageObjectModel (POM) in Playwright to improve maintainability and encapsulate common operations and page logic; 3. Jest and Playwright can jointly achieve comprehensive coverage of unit tests and end-to-end tests; 4. Playwright's TraceViewer can be used to intuitively debug failed tests. These strategies respectively optimize testing efficiency, code structure, test level coverage and debugging capabilities, and are suitable for complex projects

Bun is a modern JavaScript runtime that can replace tools such as Node.js, npm and Webpack. Its core advantage lies in speed. 1. Bun is built on Zig, using the JavaScriptCore engine, which can directly run JavaScript and TypeScript files without additional configuration; 2. It has a built-in package manager, supports installation dependencies from npm, and speeds are 10-100 times faster than npm, and generates bun.lockb lock files; 3. Built-in native packager, supports minimization, environment variables, code segmentation and other functions, which can replace Webpack or esbuild; 4. Provides a quick test runner with Jest syntax, automatically searching

To achieve real-time communication, the key to using JavaScript's WebSocket is to understand its basic usage and common scenarios. 1. Only one line of code is required to establish a connection: constsocket=newWebSocket('ws://example.com/socket');, using open, message, error, and close events to handle the connection status; 2. Send and receive data in JSON format, send through socket.send(), listen to message events to receive and parse data; 3. Handle disconnection and reconnection, you can automatically reconnect by listening to close and error events, combined with setTimeout,

ESModules (ESM) and CommonJS are two module systems of JavaScript. The main differences are syntax, loading mechanism, execution timing, environment support and interoperability. 1. Syntax, ESM uses import/export static declaration, and CommonJS uses require()/module.exports to dynamically assign values. 2. In terms of loading mechanism, ESM supports static analysis and tree-shaking. CommonJS is dynamically loaded at runtime, with high flexibility but not conducive to optimization. 3. In execution time, ESM can obtain the latest value through real-time binding; CommonJS cache module output may return part

DefinecustomerrorclasseslikeValidationErrorandDatabaseErrortoenablepreciseerrorhandlingusinginstanceofandimproveloggingconsistency.2.Usecentralizederror-handlingmiddlewareinExpress.jsbypassingerrorstonext()anddefiningaglobalerrorhandlertostandardizer