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Fundamentals · easy

2. let, const and var

Block scope and why `var` is retired.

1 min read3 questionsup to 50 XPtopic 2/50

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`let` and `const` are block-scoped: they exist only inside the nearest `{ }`. `const` forbids reassignment of the binding, though the object it points at can still be mutated. `var` is function-scoped and hoisted.

js
const chain = "Base";
let block = 1;
block += 1;

Default to `const`, reach for `let` when a value changes, and avoid `var` in modern code.

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  1. 1. What does `const` prevent?

  2. 2. What scope does `var` have?

  3. 3. Which should you default to?

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