How Does Hoisting Work Differently for `let` and `const` Compared to `var` in JavaScript?

Hoisting of Variables Declared with Let and Const

Hoisting is a JavaScript mechanism that moves declarations to the top of their scopes at the beginning of the programme's execution. However, unlike var declarations, let and const hoisting differs in terms of variable initialization.

Hoisting of Declarations

All declarations in JavaScript are hoisted, including those using var, let, const, function, function*, and class. This means that the identifier within a scope will always refer to the declared variable.

Hoisting vs. Initialization

The distinction between var/function/function* declarations and let/const/class declarations lies in their initialization. var/function/function* declarations are initialized with undefined or the function body upon binding creation at the scope's start. However, lexically declared variables (let/const/class) remain uninitialized.

Temporal Dead Zone for Let and Const

The uninitialized state of lexically declared variables creates a "temporal dead zone" where accessing them before initialization results in a ReferenceError. The temporal dead zone exists from the variable's creation until the let/const/class statement is executed.

Similarities between Let and Const

Both let and const exhibit identical hoisting behaviour. The only significant difference being that constants must be assigned only in their declaration (const one = 1;), whereas let allows reassignment.

Conclusion

While all declarations are hoisted in JavaScript, let and const variables remain uninitialized until their declaration statement is evaluated, creating a temporal dead zone. This distinction is essential to avoid referencing uninitialized variables and ensures the intended behavior of your code.

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