Junior Web Developer key terms

An HTML tag whose name describes the meaning or role of its content, such as nav, main, article, or footer, rather than only its appearance. It helps browsers, assistive technology, and search engines interpret page structure.

The hierarchy of headings and sectioning elements that describes a page's content structure. A logical outline lets screen reader users and search engines navigate and understand the page without relying on visual styling.

The ordered use of h1 through h6 so that heading levels descend without skipping, reflecting nested content. Correct hierarchy gives assistive technology users a navigable table of contents and improves search engine interpretation.

An HTML element that cannot contain child content or a closing tag, such as img, br, input, or meta. Its content, if any, comes from attributes like src or alt.

A name-value pair written inside an element's opening tag that configures the element, such as href on a link or src on an image. Boolean attributes are present or absent rather than assigned a value.

A custom attribute prefixed with data- that stores extra information on an element for scripts or styling. It is exposed through the dataset property in JavaScript and must not be used to convey essential content.

The layout rule that treats every element as a content box surrounded by padding, border, and margin. Width calculations depend on box-sizing, which determines whether padding and border are included in a declared width.

A CSS property that controls whether an element's declared width includes padding and border. Setting border-box makes sizing predictable because padding and borders are drawn inside the specified width.

A one-dimensional CSS layout model that distributes space and aligns items along a main axis and cross axis. Properties such as justify-content, align-items, and flex-grow control how children size and position.

A two-dimensional CSS layout system that places items into rows and columns defined with grid-template properties. It suits whole-page layouts where alignment in both directions matters.

A CSS rule that applies styles only when conditions about the viewport, such as width or orientation, are met. It is the main tool for responsive layouts and for honoring user preferences like reduced motion.

A strategy that writes base styles for small screens and adds enhancements at larger widths using min-width media queries. It keeps the smallest payload and simplest layout as the baseline.

An image delivered at an appropriate resolution or crop for the user's device using srcset, sizes, or the picture element. It reduces wasted bandwidth and avoids blurry or oversized images.

JavaScript's behavior of making function declarations and var bindings available before their line executes. Function declarations are fully hoisted; var is initialized as undefined, while let and const stay in a temporal dead zone.

The period between entering a scope and the declaration of a let or const variable, during which accessing it throws a ReferenceError. It makes block-scoped variables unusable before their declaration line.

A function that retains access to variables from the scope where it was created, even after that scope has finished executing. Closures power callbacks, module patterns, and private state.

The region of code where a variable is visible and usable. JavaScript has global, function, and block scope, and lexical scoping determines visibility from where code is written rather than where it runs.

The linked series of objects JavaScript consults when a property is not found on an object itself. It implements inheritance, and the chain ends at Object.prototype with a null prototype.

The value the this keyword refers to in a given function call, determined by how the function is invoked. Arrow functions do not define their own this and inherit it from the enclosing scope.

The mechanism that runs JavaScript's call stack and moves queued callbacks onto it when the stack is empty. It explains why timers and network responses run after current synchronous code completes.

A short callback queued on the microtask queue, such as a promise reaction, that runs before the next macrotask. Microtasks drain completely after each task, which affects execution order.

An object representing the eventual result of an asynchronous operation, settling once as fulfilled or rejected. It supports chaining with then and catch, and awaiting it inside async functions.

An object in the document tree representing an element, text, comment, or the document itself. Nodes expose properties and methods for reading and changing page structure and content.

A technique that attaches one listener to a common ancestor and uses event bubbling to handle events from many descendants. It reduces listener count and works for elements added later.

The default propagation phase in which an event travels from its target up through ancestor elements. Listeners on ancestors can observe it unless propagation is stopped.

A method on the event object that cancels the browser's default action, such as following a link or submitting a form. It does not stop the event from bubbling to ancestors.

The text assistive technology announces for a control, computed from sources like visible text, labels, aria-label, or aria-labelledby. Every interactive element needs a meaningful accessible name.

An attribute from the Accessible Rich Internet Applications specification that adds roles, states, or properties to markup. Native semantic elements are preferred, and ARIA must never contradict real behavior.

A page area exposed to assistive technology as a navigable region, produced by elements like header, nav, main, and footer or by equivalent ARIA roles. Landmarks let users jump between page sections.

An HTML element that associates descriptive text with a form control through for and id or by wrapping the control. Clicking the label focuses or activates the control, and screen readers announce the text.

The process of checking user input before accepting it, using HTML constraint attributes, JavaScript logic, or server-side checks. Client validation improves feedback, but servers must always validate again.

A three-digit number in a response indicating the outcome of a request, grouped into classes like 2xx success, 3xx redirect, 4xx client error, and 5xx server error. It guides client and caching behavior.

A verb in a request describing the intended action, such as GET to retrieve, POST to create, PUT to replace, PATCH to modify, or DELETE to remove. Methods carry defined safety and idempotency expectations.

A browser security mechanism that blocks cross-origin responses unless the server sends matching Access-Control-Allow-Origin headers. Preflight requests check whether a cross-origin call is permitted.

A browser rule restricting scripts from reading resources from a different scheme, host, or port than the page. It limits data theft and is relaxed deliberately through CORS or postMessage.

A snapshot of the project's tracked changes recorded with a message, author, timestamp, and a hash identifying it. Commits form a history that branches and merges build on.

A state where Git cannot automatically combine changes because two branches edited the same lines. The developer resolves markers manually, then stages and commits the result.

A hosted-repository proposal to merge a branch into another, enabling review, discussion, and automated checks before integration. It is a workflow convention, not a core Git command.

An attack that injects malicious script into pages viewed by other users, often through unsanitized input. Defenses include output encoding, safe DOM APIs, and a strict Content Security Policy.

An HTTP response header that restricts which sources may load scripts, styles, images, and other resources, and whether inline code may run. It reduces the impact of injected scripts.

A unique, unpredictable value embedded in a form or request and verified server-side to prove the request came from the site's own pages. It blocks forged cross-site state-changing requests.

An automated test that exercises one small piece of code, such as a function, in isolation with controlled inputs and asserted outputs. It runs fast and pinpoints failures precisely.

A statement in a test declaring an expected result, which fails the test when the actual value differs. Clear assertions make failures self-explanatory.

A test written to confirm that a previously fixed bug stays fixed or that existing behavior survives a change. Regression suites protect against reintroducing known defects.

A marker set in developer tools or source code that pauses execution at a chosen line so state can be inspected. Stepping and watch expressions then reveal how values change.