Glossary

JavaScript glossary

60 terms found

Glossaries

All CSS HTML JavaScript Programming

2xx

JavaScript

Family of HTTP status codes that normally indicates a successful request.

A `201 Created` response belongs to the 2xx range.

4xx

JavaScript

Family of HTTP status codes that usually indicates a client-side problem with the request.

A `404 Not Found` response belongs to the 4xx range.

5xx

JavaScript

Family of HTTP status codes that usually indicates a server-side failure.

A `500 Internal Server Error` response belongs to the 5xx range.

Accept

JavaScript

Header that tells the server which response formats the client can handle.

A request can send `Accept: application/json` to ask for JSON data.

AJAX

JavaScript

Approach for sending asynchronous HTTP requests so parts of a page can update without a full reload.

A search box that shows suggestions while you type is often using an AJAX-style request flow.

API

JavaScript

Set of rules and endpoints that allows one system to communicate with another.

A frontend application can call an API to fetch products or save form data.

API Versioning

JavaScript

Strategy for evolving an API without breaking clients that depend on older behavior.

An API can expose `/v1/users` and `/v2/users` while teams migrate gradually.

BOM

JavaScript

Browser Object Model. Collection of browser-specific objects such as `window`, `history` and `location`.

Reading `window.location.pathname` is interacting with the BOM.

Bubbling

JavaScript

Phase of event propagation where an event moves from the target element back up through its ancestors.

A click on a button can bubble to its parent card and then to the document.

Capturing

JavaScript

Phase of event propagation where an event travels from higher ancestors down toward the target element.

A listener registered for capture can run before the target phase of a click event.

Closure

JavaScript

Function that keeps access to variables from its lexical scope even after that outer scope has finished executing.

A counter function that remembers an internal `count` variable is using a closure.

Code Splitting

JavaScript

Optimization technique that breaks a large JavaScript bundle into smaller chunks loaded on demand.

An admin panel can load chart-related code only when the charts page is opened.

Content-Type

JavaScript

Header that describes the format of the request or response body.

When sending JSON, the client often sets `Content-Type: application/json`.

Cookie

JavaScript

Small piece of data stored by the browser and often used for sessions, preferences or tracking.

A site may store a session identifier in a cookie after login.

Debounce

JavaScript

Pattern that delays a function call until activity stops for a defined amount of time.

A search input can debounce requests so the API is called only after the user pauses typing.

DELETE

JavaScript

HTTP method commonly used to remove a resource on the server.

A `DELETE /tasks/8` request can remove one task from a list.

DOM

JavaScript

Document Object Model. The browser representation of the HTML document as a tree of nodes that JavaScript can read and modify.

Changing the text of a heading with `textContent` is a DOM update.

Endpoint

JavaScript

Specific URL where an API exposes a resource or an operation.

The endpoint `/api/orders` can return the order list.

Event Delegation

JavaScript

Pattern where a parent element handles events for its children through bubbling.

A task list can use one click listener on the `<ul>` instead of one listener per button.

Event Loop

JavaScript

Mechanism that coordinates the call stack, task queue and microtask queue in JavaScript runtimes.

It explains why a resolved promise callback usually runs before a `setTimeout(..., 0)` callback.

Exponential Backoff

JavaScript

Retry strategy where the waiting time grows after each failed attempt.

A request can wait 1 second, then 2, then 4 before trying again.

Express

JavaScript

Minimal framework for building web servers and APIs with Node.js.

You can use Express to create routes such as `/users` or `/posts` in a backend project.

Fetch

JavaScript

Modern browser API used to make HTTP requests from JavaScript.

You can use `fetch('/api/products')` to retrieve a list of products from a server.

FormData

JavaScript

Browser API that reads form fields and builds a data structure ready to send or transform.

You can turn a form into an object with `Object.fromEntries(new FormData(form).entries())`.

Graceful Degradation

JavaScript

Approach where a rich experience is built first and then degrades acceptably in less capable environments.

An advanced animation might fall back to a simpler visual effect in an older browser.

Hoisting

JavaScript

JavaScript behavior where declarations are processed before code execution reaches their line.

A function declaration can often be called before its visible position in the file.

HTTP Status Code

JavaScript

Numeric code returned by a server to explain the outcome of an HTTP request.

A response with code 200 usually means the request succeeded.

JavaScript

Programming language used to add logic, behavior and interactivity to web pages and web applications.

A form that validates user input in real time is using JavaScript.

JSON

JavaScript

Lightweight data format used to exchange structured information between applications.

APIs often return product lists or user data in JSON format.

Lazy Loading

JavaScript

Technique that delays loading code or assets until they are actually needed.

A gallery can defer heavy images until the user scrolls near them.

Literal

JavaScript

Direct value written in code, such as a string, number, array or object.

`42`, `'hello'` and `{ active: true }` are all literals.

LocalStorage

JavaScript

Browser storage mechanism for persisting small string-based values across sessions.

A theme preference can be saved in `localStorage` so it survives a page reload.

MutationObserver

JavaScript

Browser API that watches DOM changes and lets your code react to them.

A widget can observe when new items are inserted into a list and update counters automatically.

NaN

JavaScript

Special JavaScript value that means Not a Number.

Trying to convert an invalid numeric string can produce `NaN`.

NodeList

JavaScript

Collection of DOM nodes returned by methods such as `querySelectorAll()`.

A `NodeList` of buttons can be looped through to attach behavior or update classes.

Offset Pagination

JavaScript

Pagination model where the client requests items using an offset and a limit.

A request such as `?offset=40&limit=20` asks for the next block of 20 items after the first 40.

Pagination

JavaScript

Technique that divides large result sets into smaller pages instead of loading everything at once.

An ecommerce grid can show 20 products per page with next and previous controls.

PATCH

JavaScript

HTTP method commonly used to apply a partial update to an existing resource.

A `PATCH /profile` request can update only the user's avatar without replacing the whole profile.

Polyfill

JavaScript

Code that adds support for a modern feature in environments that do not implement it natively.

A polyfill can provide `Array.prototype.includes` in an older browser.

preventDefault

JavaScript

Method on the event object that stops the browser's default action for that event.

Calling `preventDefault()` on a form submit lets you validate before a real request is sent.

Promise

JavaScript

Object that represents the future completion or failure of an asynchronous operation.

A `fetch()` call returns a promise that resolves when the response arrives.

Proxy

JavaScript

JavaScript object that intercepts operations on another object, such as reading or writing properties.

A proxy can log every property access on a configuration object for debugging.

PUT

JavaScript

HTTP method commonly used to replace or fully update a resource.

A `PUT /products/42` request may send the full product representation.

Race Condition

JavaScript

Bug that appears when the final result depends on which asynchronous operation finishes first.

Two overlapping searches can return out of order and display stale results if you do not control the flow.

Rate Limiting

JavaScript

Restriction that limits how many requests or actions can happen in a given period.

An API might allow only 100 requests per minute from one client.

Request Header

JavaScript

HTTP metadata sent with a request to describe how it should be processed.

An `Authorization` header can carry an access token when calling an API.

REST API

JavaScript

API style that organizes resources and operations around HTTP methods such as GET, POST, PUT and DELETE.

A REST API might expose `/products` to list items and `/products/42` to update one item.

Retry

JavaScript

Practice of repeating a failed request when the error may be temporary.

A client can retry a request after a transient network failure or a `503` response.

Serialization

JavaScript

Process of converting data structures into a format that can be stored or transmitted.

Turning an object into a JSON string before sending it over HTTP is serialization.

SPA

JavaScript

Single Page Application. A web app that updates content dynamically without doing a full page reload on every interaction.

A dashboard that changes sections instantly while staying on one document is behaving like an SPA.

stopPropagation

JavaScript

Method on the event object that prevents an event from continuing its propagation through the DOM.

A nested button can stop a click from reaching a parent card listener.

Strict Mode

JavaScript

Restricted JavaScript mode that catches certain mistakes earlier and disables some risky legacy behaviors.

Strict mode throws when you assign to an undeclared variable instead of creating it implicitly.

TDZ

JavaScript

Temporal Dead Zone. Period in which a `let` or `const` variable exists but cannot be accessed before its declaration line runs.

Reading a `let` variable before its declaration can throw a `ReferenceError` because of the TDZ.

Throttle

JavaScript

Pattern that limits how often a function can run within a time interval.

A scroll handler can be throttled so it runs at most once every 100 milliseconds.

Timeout

JavaScript

Maximum time the client allows an operation or request to take before treating it as failed.

A fetch wrapper can cancel the request if no response arrives after 8 seconds.

Tree Shaking

JavaScript

Build optimization that removes unused exported code from the final bundle.

If you import only one helper from a module, tree shaking can avoid shipping the rest.

URLSearchParams

JavaScript

API for reading and building query string parameters in a structured way.

You can use `URLSearchParams` to read `?page=2&sort=price` from the current URL.

Validation

JavaScript

Process of checking whether input data meets the expected rules before it is accepted or sent.

A signup form can validate that an email contains `@` and a password has a minimum length.

Web API

JavaScript

Browser-provided interface that extends JavaScript with capabilities such as networking, storage and DOM access.

`fetch`, `localStorage` and `MutationObserver` are examples of Web APIs.

Webpack

JavaScript

Bundler that analyzes project dependencies and produces optimized files for the browser.

Webpack can combine modules, split chunks and generate production-ready bundles.