JS FAQ - JavaScript Guides Online

Async and await in Jest enable clean asynchronous testing by returning promises that Jest automatically waits to resolve. Use try/catch for error handling or Jest’s rejects matcher for concise rejection tests. Combining await with Promise.all improves parallel execution and test efficiency.

Standard Objects: RegExp

How to extract all matches using regex in JavaScript

Standard Objects: RegExpglobal, js regexp, matchAll, regexp

The string.match method returns matched substrings or null, with behavior dependent on the global flag. Without 'g', it returns the first match and capturing groups. With 'g', it returns all matches without groups. For capturing groups on all matches, use RegExp.exec in a loop or matchAll with 'g'.

Crypto and Utilities

How to generate cryptographically secure random numbers in Node.js

Crypto and Utilitiescrypto, node.js, randomBytes, secure

The crypto module in Node.js offers secure random number generation methods like randomBytes and randomUUID, essential for creating cryptographic keys, tokens, session IDs, and unique identifiers. These methods provide cryptographically strong randomness not achievable with Math.random().

Libraries: TensorFlow.js

How to create a tensor in TensorFlow.js

Libraries: TensorFlow.jsdata, shape, tensor, tensorflowjs

Manipulating tensor shapes in TensorFlow.js involves reshaping, transposing, slicing, and concatenating tensors to meet specific input requirements for neural networks. Functions like tf.transpose and tensor.cast enable dimension permutations and type conversions, essential for advanced deep learning workflows. Understanding these operations is crucial for efficient model construction.

Variables and Types

How to check the data type of a variable in JavaScript

Variables and Typesjs types, primitives, typeof, types

instanceof operator in JavaScript checks if an object is an instance of a constructor, useful for distinguishing arrays from objects. Cross-context issues arise with iframes, where instanceof may fail. Combining instanceof with constructor checks enhances reliable type detection across environments.

Standard Objects: Array

How to extract a substring using substr in JavaScript

Standard Objects: Arrayjs string, legacy, string, substr

File name handling with substr simplifies extraction of file extensions and fixed-width tokens from logs. Using lastIndexOf with substr efficiently retrieves components without pre-calculation. Negative indices and a safe wrapper enhance usability, preventing out-of-bounds errors. Substr truncates decimal parameters, allowing seamless handling of float-based lengths.

Standard Objects: String

How to extract a substring using substring in JavaScript

Standard Objects: Stringextract, js string, string, substring

String manipulation with JavaScript substring enables efficient extraction of domains, file extensions, timestamps, usernames, and truncated text. Combining substring with indexOf or lastIndexOf avoids regex complexity, ensures precise slicing, and handles dynamic or fixed-width inputs in parsing and UI scenarios.

Classes and Inheritance

How to set default values in a class constructor in JavaScript

Classes and Inheritanceclass, constructor, defaults, js classes

Constructing a robust JavaScript application requires managing undefined values in constructors. Utilizing the nullish coalescing operator for default assignments enhances clarity. Placing defaults in parameter lists simplifies code and signals expected behavior. Thoughtful design choices regarding default values lead to more maintainable applications.

Node.js Core

How to import a module using ES modules in Node.js

Node.js Coreesm, import, js modules, node.js

Node.js distinguishes between CommonJS and ES modules using file extensions and the package.json type field. By default, .js files are CommonJS unless "type": "module" is set in package.json. The .mjs extension explicitly marks ES modules. Understanding these distinctions ensures proper module resolution and prevents errors in Node.js applications.

Event Loop Internals

How to understand macrotasks in JavaScript

Event Loop Internalsevent loop, macrotask, setTimeout

JavaScript event loop separates macrotasks and microtasks, affecting timing functions like setTimeout and Promise.then. Macrotasks run sequentially, possibly blocking UI, while microtasks execute immediately after macrotasks, enabling fast async completions and precise control over task sequencing.