Want to be a software engineer? The difficulty of top down learning.

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.

Functional programming (FP) is suitable for data immutable scenarios, emphasizing pure functions and no side effects, and is suitable for processing data transformations such as array mapping or filtering; Object-oriented programming (OOP) is suitable for modeling real-world entities, encapsulating data and behaviors through classes and objects, and is suitable for managing objects with state such as bank accounts; JavaScript supports the use of the two, and selecting appropriate paradigms according to needs to improve code quality. 1.FP is suitable for scenarios where data transformation and state remains unchanged, making it easy to test and debug. 2.OOP is suitable for modeling entities with identity and internal state, providing a good organizational structure. 3. JavaScript allows the mixing of FP and OOP, using their respective advantages to improve maintainability.

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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.

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.

Callback hell refers to nested callbacks that make the code difficult to maintain. The solution is to use Promise or async/await. 1. Promise replaces nested structures through chain calls, making the logic clear and error handling unified; 2. async/await is based on Promise, writing asynchronous code in a synchronous way to improve readability and debugging experience; 3. In actual applications, you need to pay attention to the single function responsibilities, use Promise.all in parallel tasks, correctly handle errors and avoid abuse of async/await.