Does the JavaScript engine physically move code to the top?
No. Hoisting is a mental model. The engine does not rearrange source code. It scans once for declarations, reserves memory, and then runs the code line-by-line.
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More FAQs in Why JavaScript Hoists Variables and Functions
Because the engine allocates memory for all declarations during the memory allocation phase of execution context creation, before any code runs. This is a side effect, not a feature. It allows forward references and faster execution.
So that functions can be called from anywhere in the scope, regardless of order. If the engine waited to store a function until its declaration line, calls earlier in the file would fail.
var was designed for loose, forgiving code (pre-ES6). let and const were introduced in ES6 to catch bugs early. The TDZ makes accessing a variable before declaration an error instead of silently returning undefined.
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