React Testing: A Comprehensive Guide

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.

Hello, JavaScript developers! Welcome to this week's JavaScript news! This week we will focus on: Oracle's trademark dispute with Deno, new JavaScript time objects are supported by browsers, Google Chrome updates, and some powerful developer tools. Let's get started! Oracle's trademark dispute with Deno Oracle's attempt to register a "JavaScript" trademark has caused controversy. Ryan Dahl, the creator of Node.js and Deno, has filed a petition to cancel the trademark, and he believes that JavaScript is an open standard and should not be used by Oracle

CacheAPI is a tool provided by the browser to cache network requests, which is often used in conjunction with ServiceWorker to improve website performance and offline experience. 1. It allows developers to manually store resources such as scripts, style sheets, pictures, etc.; 2. It can match cache responses according to requests; 3. It supports deleting specific caches or clearing the entire cache; 4. It can implement cache priority or network priority strategies through ServiceWorker listening to fetch events; 5. It is often used for offline support, speed up repeated access speed, preloading key resources and background update content; 6. When using it, you need to pay attention to cache version control, storage restrictions and the difference from HTTP caching mechanism.

Promise is the core mechanism for handling asynchronous operations in JavaScript. Understanding chain calls, error handling and combiners is the key to mastering their applications. 1. The chain call returns a new Promise through .then() to realize asynchronous process concatenation. Each .then() receives the previous result and can return a value or a Promise; 2. Error handling should use .catch() to catch exceptions to avoid silent failures, and can return the default value in catch to continue the process; 3. Combinators such as Promise.all() (successfully successful only after all success), Promise.race() (the first completion is returned) and Promise.allSettled() (waiting for all completions)

JavaScript array built-in methods such as .map(), .filter() and .reduce() can simplify data processing; 1) .map() is used to convert elements one to one to generate new arrays; 2) .filter() is used to filter elements by condition; 3) .reduce() is used to aggregate data as a single value; misuse should be avoided when used, resulting in side effects or performance problems.

JavaScript's event loop manages asynchronous operations by coordinating call stacks, WebAPIs, and task queues. 1. The call stack executes synchronous code, and when encountering asynchronous tasks, it is handed over to WebAPI for processing; 2. After the WebAPI completes the task in the background, it puts the callback into the corresponding queue (macro task or micro task); 3. The event loop checks whether the call stack is empty. If it is empty, the callback is taken out from the queue and pushed into the call stack for execution; 4. Micro tasks (such as Promise.then) take precedence over macro tasks (such as setTimeout); 5. Understanding the event loop helps to avoid blocking the main thread and optimize the code execution order.

Event bubbles propagate from the target element outward to the ancestor node, while event capture propagates from the outer layer inward to the target element. 1. Event bubbles: After clicking the child element, the event triggers the listener of the parent element upwards in turn. For example, after clicking the button, it outputs Childclicked first, and then Parentclicked. 2. Event capture: Set the third parameter to true, so that the listener is executed in the capture stage, such as triggering the capture listener of the parent element before clicking the button. 3. Practical uses include unified management of child element events, interception preprocessing and performance optimization. 4. The DOM event stream is divided into three stages: capture, target and bubble, and the default listener is executed in the bubble stage.