`window.onload vs. $(document).ready(): When Should I Use Each?`

There are three common ways to initiate HTTP requests in Node.js: use built-in modules, axios, and node-fetch. 1. Use the built-in http/https module without dependencies, which is suitable for basic scenarios, but requires manual processing of data stitching and error monitoring, such as using https.get() to obtain data or send POST requests through .write(); 2.axios is a third-party library based on Promise. It has concise syntax and powerful functions, supports async/await, automatic JSON conversion, interceptor, etc. It is recommended to simplify asynchronous request operations; 3.node-fetch provides a style similar to browser fetch, based on Promise and simple syntax

JavaScript data types are divided into primitive types and reference types. Primitive types include string, number, boolean, null, undefined, and symbol. The values are immutable and copies are copied when assigning values, so they do not affect each other; reference types such as objects, arrays and functions store memory addresses, and variables pointing to the same object will affect each other. Typeof and instanceof can be used to determine types, but pay attention to the historical issues of typeofnull. Understanding these two types of differences can help write more stable and reliable code.

In JavaScript arrays, in addition to map and filter, there are other powerful and infrequently used methods. 1. Reduce can not only sum, but also count, group, flatten arrays, and build new structures; 2. Find and findIndex are used to find individual elements or indexes; 3.some and everything are used to determine whether conditions exist or all meet; 4.sort can be sorted but will change the original array; 5. Pay attention to copying the array when using it to avoid side effects. These methods make the code more concise and efficient.

The filter() method in JavaScript is used to create a new array containing all the passing test elements. 1.filter() does not modify the original array, but returns a new array that meets the conditional elements; 2. The basic syntax is array.filter((element)=>{returncondition;}); 3. The object array can be filtered by attribute value, such as filtering users older than 30; 4. Support multi-condition filtering, such as meeting the age and name length conditions at the same time; 5. Can handle dynamic conditions and pass filter parameters into functions to achieve flexible filtering; 6. When using it, be careful to return boolean values ​​to avoid returning empty arrays, and combine other methods to achieve complex logic such as string matching.

In JavaScript, check whether an array contains a certain value. The most common method is include(), which returns a boolean value and the syntax is array.includes(valueToFind), for example fruits.includes('banana') returns true; if it needs to be compatible with the old environment, use indexOf(), such as numbers.indexOf(20)!==-1 returns true; for objects or complex data, some() method should be used for in-depth comparison, such as users.some(user=>user.id===1) returns true.

Virtual DOM is a programming concept that optimizes real DOM updates. By creating a tree structure corresponding to the real DOM in memory, it avoids frequent and direct operation of real DOM. Its core principle is: 1. Generate a new virtual DOM when the data changes; 2. Find the smallest difference between the new and old virtual DOMs; 3. Batch update of the real DOM to reduce the overhead of rearrangement and redrawing. In addition, using a unique stable key can improve list comparison efficiency, while some modern frameworks have adopted other technologies to replace virtual DOM.

To handle errors in asynchronous functions, use try/catch, handle them in the call chain, use the .catch() method, and listen for unhandledrejection events. 1. Use try/catch to catch errors is the recommended method, with a clear structure and can handle exceptions in await; 2. Handling errors in the call chain can be centralized logic, which is suitable for multi-step processes; 3. Use .catch() to catch errors after calling async function, which is suitable for Promise combination scenarios; 4. Listen to unhandledrejection events to record unhandled rejections as the last line of defense; the above methods jointly ensure that asynchronous errors are correctly captured and processed.

The key to dealing with JavaScript time zone issues is to choose the right method. 1. When using native Date objects, it is recommended to store and transfer in UTC time and convert it to the user's local time zone when displaying; 2. For complex time zone operations, moment-timezone can be used, which supports IANA time zone database and provides convenient formatting and conversion functions; 3. If you need to localize the display time and do not want to introduce third-party libraries, you can use Intl.DateTimeFormat; 4. It is recommended to modern lightweight solution day.js and timezone and utc plug-in, which has a concise API, good performance and supports timezone conversion.