List of programming languages
A Map is JavaScript’s dedicated key-value data structure. Unlike plain objects, a Map can use any value as a key — objects, functions, numbers, even other maps — and it preserves insertion order for iteration. It’s the modern replacement for using objects as dictionaries. Key point: Use Map when your keys aren’t strings, when you…
These two media features let you adapt styles for monochrome displays and screen orientation — one for specialized devices, the other for everyday responsive design. Overview of Features Feature Description Values monochrome Bits per pixel for monochrome devices Integer (0, 1, 8) orientation Portrait or landscape orientation portrait, landscape 1. monochrome The monochrome media feature…
The instanceof operator checks whether an object was created by a specific constructor — or more precisely, whether that constructor’s prototype appears anywhere in the object’s prototype chain. It’s the standard way to ask “is this a Date?”, “is this an Array?”, “is this a Dog?”. Key point: instanceof walks the prototype chain. If the…
These two media features describe how a device handles content overflow — whether it scrolls, paginates, or simply clips. They’re especially relevant for paged media (like print) and e-readers. Overview of Features Feature Description Axis overflow-block Overflow handling along the block axis Vertical (in horizontal writing modes) overflow-inline Overflow handling along the inline axis Horizontal…
Errors are a normal part of every program — files go missing, networks drop, users type nonsense, and code has bugs. JavaScript gives you a structured way to throw, catch, and handle errors so a single failure doesn’t crash the whole app. The try / catch / finally block is the foundation of that system….
These two media features let you adapt styles based on the accuracy of the pointing device and the pixel density of the display — essential for touch-friendly interfaces and high-DPI screens. Overview of Features Feature Description Values pointer Accuracy of the primary pointing device none, coarse, fine resolution Pixel density of the output device dpi,…
The this keyword is one of the most confusing parts of JavaScript — until you understand one simple rule: this is determined by how a function is called, not where it’s defined. Once you internalize that rule, everything else falls into place. Key point: this refers to the execution context of a function — the…
These two media features are essential for accessibility and personalization. They let you respect the user’s preferred color scheme (light/dark) and contrast level. Overview of Features Feature Description Values prefers-color-scheme User’s preferred color scheme light, dark prefers-contrast User’s preferred contrast level no-preference, more, less, custom 1. prefers-color-scheme The prefers-color-scheme media feature detects whether the user…
The spread operator (…) takes an iterable — an array, a string, a Set, a Map — or an object, and expands its contents into individual elements. It’s the opposite of the rest parameter, which collects values into an array. Same syntax, different purpose. Key point: Spread expands; rest collects. Both use …, and the…
These two media features prioritize user comfort and performance. One respects users who want less data usage, the other respects users who are sensitive to motion. Overview of Features Feature Description Values prefers-reduced-data User wants lighter data usage no-preference, reduce prefers-reduced-motion User wants less animation/motion no-preference, reduce 1. prefers-reduced-data The prefers-reduced-data media feature detects if…
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