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JavaScript const keyword

  1. const keyword always creates a value which is scoped to the block in which it is declared.
  2. Values created using const are not mutable by value or reference.
  3. So, all primitive values created using const can never be replaced by another value.
  4. For non primitive values like objects and arrays, their references cannot be changed, but still they can be mutated.

This 4th point has always been tricky for new comers to JavaScript.

const x = 10;
x = 20; // fails
const user = {
x: 10
user.x = 20; // works
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