How do var, let, and const differ in scope, initialization, and reassignment?

Compares JavaScript declarations through scope, initialization, redeclaration, reassignment, and practical default choices.

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TL;DR

var is function-scoped, can be redeclared, and reads as undefined before its declaration is executed. let and const are block-scoped and cannot be used before initialization; that interval is the temporal dead zone. let can be reassigned, while const cannot. const protects the binding, not the contents of an object stored in it.

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Whether the candidate understands declaration behavior rather than repeating that const means immutable.

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Core answer
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Overview
The useful comparison is about bindings and scope. const does not freeze an object, and hoisting does not make every declaration safely readable early.
var is function-scoped, can be redeclared, and reads as undefined before its declaration is executed. let and const are block-scoped and cannot be used before initialization; that interval is the temporal dead zone. let can be reassigned, while const cannot. const protects the binding, not the contents of an object stored in it.

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Common mistakesCandidateCommon mistakesMistakes that weaken the answer or signal shallow understanding.Open details

Details

Saying const makes an object immutable.
Calling let and const unhoisted without explaining the temporal dead zone.

How do var, let, and const differ in scope, initialization, and reassignment?

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