JavaScript Fundamentals
More to discover ↗JavaScript numbers are convenient, but decimal arithmetic, rounding, and large integers can produce surprising results. Learn how to recognize those limits and choose appropriate checks for everyday code.
Read article · 3 min↗Set and Map solve different collection problems. Learn when to use each, how their equality rules work, and where arrays and plain objects remain simpler choices.
Read article · 4 min↗JSON is a useful format for moving data between systems, but JavaScript objects do not always survive a JSON round trip unchanged. Learn which values JSON supports, what JSON.stringify omits or converts, and how to handle JSON.parse errors.
Read article · 4 min↗Learn how JavaScript errors move through a program, when to throw your own Error, how to handle a failure with try and catch, and where finally fits into cleanup. Examples work in a modern browser console or a recent Node.js environment.
Read article · 4 min↗Learn how JavaScript promises carry future results, how async/await makes dependent steps easier to read, and when independent operations can run together. Reproducible examples use only features available in a modern browser console or a current Node.js environment.
Read article · 4 min↗ES modules let you divide JavaScript into files with clear responsibilities. Learn when to use named or default exports, how to import them, and how to run a small browser example without common path and loading mistakes.
Read article · 3 min↗A JavaScript class provides a convenient way to create objects, but method sharing still happens through prototypes. Learn where properties live, how lookup works, and how to inspect the chain with a small reproducible example.
Read article · 4 min↗The value of this depends on how a regular function is called, while an arrow function takes this from where it was created. Learn how that difference affects methods, callbacks, event listeners, and common fixes for lost context.
Read article · 4 min↗A closure lets a JavaScript function use variables from the place where it was created, even after the surrounding function returns. Learn how lexical scope works, why captured values can change, and where closures are useful in everyday code.
Read article · 4 min↗Learn what happens when a JavaScript function receives fewer or more arguments than expected, how default and rest parameters work, and why an explicit return value makes a function easier to use.
Read article · 3 min↗Learn how to unpack arrays and objects with destructuring, gather remaining values with rest syntax, and use spread syntax to create shallow copies. Practical examples show where defaults help and where nested references still matter.
Read article · 4 min↗Learn when to use bracket notation for dynamic property names and when optional chaining prevents a missing object from throwing an error. Reproducible examples show how to combine both forms, provide defaults, and distinguish a missing property from a property whose value is undefined.
Read article · 4 min↗Use map when every item becomes a new value, filter when some items should be kept, and reduce when many items must become one result. A small, runnable example shows how to choose between them and avoid common mistakes.
Read article · 4 min↗Learn which array methods change the original array and which return a copy. Use slice, splice, sort, toSpliced, and toSorted to make updates predictable, with examples that also explain shallow copying and browser compatibility.
Read article · 4 min↗These three loops answer different questions: do you need an index, a value from an iterable, or a property name? Learn how to choose a loop for arrays, strings, and objects, and where sparse arrays and inherited properties can surprise you.
Read article · 4 min↗JavaScript offers several ways to choose between outcomes. Learn when an if statement, a switch statement, or the conditional operator makes a branch easiest to understand, with examples you can run in a modern browser console or Node.js.
Read article · 4 min↗Learn how to build readable strings with template literals, extract text with slice(), and avoid off-by-one and Unicode indexing surprises. Examples run in a modern browser console or a Node.js environment that supports modern JavaScript.
Read article · 4 min↗The || and ?? operators can both provide fallback values, but they disagree about when a fallback is needed. Learn how to preserve meaningful values such as 0, false and an empty string while still handling missing data.
Read article · 4 min↗JavaScript has three common ways to compare values, and they do not always agree. Learn how type conversion, NaN, signed zero, and object identity affect the result, with examples you can run in a browser console.
Read article · 4 min↗Learn when to use String(), Number(), and Boolean(), why some inputs produce surprising results, and how to validate numeric text before it becomes NaN.
Read article · 4 min↗Why does changing one variable sometimes affect another? Learn how JavaScript copies primitive values, shares references to objects, and handles mutation, reassignment, and shallow copies.
Read article · 4 min↗Learn how JavaScript’s three variable declarations differ, with small examples you can run in a browser console. See when reassignment is allowed, why blocks matter, and what “hoisting” means in practice.
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