Beyond the basics, JavaScript has a handful of core concepts that show up in every interview and every real-world project. Master these and the rest is mechanics.
Concept map
- Event loop — The runtime that processes the macrotask queue, microtask queue, and the Web APIs.
- Hoisting — `var` and function declarations are moved to the top of their scope at parse time.
- Closures — Functions retain access to the variables of the lexical scope in which they were created — the foundation for data encapsulation and currying.
- Prototypes — Every object has an internal `[[Prototype]]` chain for property lookup.
How the concepts fit together
The concepts above are not independent — they layer. The first defines the foundation, the second defines how work moves through the system, the third defines how it is observed, and the fourth defines how it is protected. Skip this layering and you will spend years relearning what one weekend of structured study would have taught you.
Code illustration
# Most JavaScript examples reduce to this shape
from javascript import core
result = core.do_thing(input_value)
assert result.is_valid()Summary
If you can describe each core concept in one sentence and sketch the code that uses it, you already beat most candidates.