list of programming languages
A Promise is JavaScript’s way of representing a value that isn’t available yet but will be — or won’t be — at some point in the future. It’s the foundation of modern asynchronous code, and it solves the “callback hell” problem that plagued JavaScript before ES6. Key point: A Promise is an object with three…
Every database query needs a connection. The naive approach is to open a connection for each query, run the query, and close the connection. The problem is that opening a connection is expensive: the TCP handshake, the TLS negotiation, the authentication, and the database’s own session setup all take time. For a PostgreSQL connection, the…
Every reference in Rust has a lifetime. A lifetime is the scope for which a reference is valid, and it is the compiler’s mechanism for preventing dangling references — references that point to data that no longer exists. The borrow checker is the part of the compiler that tracks lifetimes, and its job is to…
Every set operation answers a question about two collections. UNION asks “what is in either?” INTERSECT asks “what is in both?” And EXCEPT asks “what is in the first but not the second?” This last question—finding what is missing, what has changed, what exists in one place but not another—is one of the most common…
TypeScript’s type system is structural, not nominal. This is a deliberate design choice that matches how JavaScript is typically written — objects and functions are compared by their shape, not by their declared name. But structural typing has a real cost: two values that are structurally identical are interchangeable to the compiler, even when they…
These two media features address accessibility (transparency preferences) and legacy display technology (interlaced vs progressive scanning). Overview of Features Feature Description Values prefers-reduced-transparency User wants less transparency no-preference, reduce scan Monitor’s scanning process interlaced, progressive 1. prefers-reduced-transparency The prefers-reduced-transparency media feature detects if the user has requested reduced transparency — important for users who have…
A generator is a function that produces a sequence of values lazily. Instead of building a list and returning it, the function yields values one at a time, and the consumer receives them as they are produced. Dart has two kinds of generators: synchronous generators marked with sync*, which return an Iterable, and asynchronous generators…
async and await are the syntax sugar on top of Promises that makes asynchronous code read like synchronous code. Instead of chaining .then() calls, you write await in front of a Promise — and the function pauses until the Promise settles, without blocking the rest of the program. Key point: async marks a function as…
MongoDB stores documents, and Node.js works with objects. The two are close cousins: a MongoDB document is a BSON object, and a Node.js application is full of JavaScript objects. But the similarity is deceptive. MongoDB accepts any valid BSON document, so a collection can contain documents with different fields, different types, and different structures. For…
The previous chapter introduced lifetimes as the compiler’s mechanism for preventing dangling references. This chapter is about the syntax and the patterns. The ‘a annotation is not a runtime value and it is not a memory address. It is a name for a region of code, and the compiler uses it to reason about how…