JavaScript Fundamentals
The language itself, from variables and control flow through functions, arrays, objects, and error handling. The bedrock skills every frontend engineer uses daily.
var, let, const — what actually happens under the hood. The 7 primitives, typeof quirks, type coercion traps, and why almost everything should be const.
Every operator in JavaScript evaluated — arithmetic, assignment, comparison, logical, nullish coalescing, optional chaining, ternary, comma, and the precedence rules that tie them all together.
if/else, switch/case, for, while, for...of vs for...in, break, continue, and labeled statements. How JavaScript decides what to run next and how to repeat it efficiently.
Function declarations, expressions, and arrows — not just syntax, but the behavioral differences that trip up interviews. Parameters, rest/spread, default values, first-class functions, IIFEs, and pure functions.
Everything about JavaScript arrays — creating them, mutating them, transforming them, and choosing the right method for the job. The toolkit you'll use in every single codebase.
How objects actually work in JavaScript — from creating them to reading, checking, copying, and locking down their properties. The foundational patterns you'll use in every codebase.
How to unpack values from arrays and objects, merge data with spread, and why these two features using the same ... syntax do opposite things.
Master every string and number method you'll actually use. Understand string immutability, template literals, floating-point quirks, and the Math object — with the mental models that make it all stick.
How JavaScript errors work, the try/catch/finally execution flow, built-in error types, throwing custom errors, and patterns that separate beginners from professionals.
How JavaScript modules work — named exports, default exports, live bindings, dynamic import(), re-exporting, and the patterns that keep large codebases sane.
12 carefully crafted predict-the-output challenges covering every topic in JavaScript Fundamentals. Test your mental model before moving on.