FrontendHaltJavaScript·Intermediate·Coding·1 min read
What happens before a function body executes?
Short interview answer
The runtime establishes parameter bindings, local declarations, the lexical environment, and this according to the function's call form. Function declarations are initialized early; let, const, and class bindings exist but remain uninitialized until evaluation reaches them.
Example
foo(); // "hoisted" — declaration is ready before this lineconsole.log(x); // undefined — `var x` exists, not yet assignedvar x = 10;function foo() { console.log('hoisted'); }Key takeaway
Explain the underlying mental model clearly, then support it with a concrete example and its trade-offs.