What is the difference between `let`, `const`, and `var` in JavaScript?
302
I am new to JavaScript and I keep seeing `let`, `const`, and `var` used for variable declarations. What are the key differences between them, and when should I use each?
I understand that `const` is for values that won't be reassigned, but the difference between `let` and `var` is less clear to me, especially regarding scope.
I understand that `const` is for values that won't be reassigned, but the difference between `let` and `var` is less clear to me, especially regarding scope.
javascript
es6
variables
scope
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javascript
es6
variables
Asked about 2 years ago
BOBob The Builder
2 Answers
250
`var` is function-scoped or globally-scoped, can be re-declared and updated. It's generally not recommended in modern JS.
`let` is block-scoped, can be updated but not re-declared within the same scope.
`const` is block-scoped, cannot be updated or re-declared. The value itself can be mutable if it's an object or array, but the variable binding cannot change.
`let` is block-scoped, can be updated but not re-declared within the same scope.
`const` is block-scoped, cannot be updated or re-declared. The value itself can be mutable if it's an object or array, but the variable binding cannot change.
answered about 2 years ago by
ALAlice Wonderland
150
Key differences:
- **Scope**: `var` is function-scoped, `let` and `const` are block-scoped.
- **Hoisting**: `var` declarations are hoisted and initialized with `undefined`. `let` and `const` are hoisted but not initialized (Temporal Dead Zone).
- **Re-declaration**: `var` allows re-declaration in the same scope. `let` and `const` do not.
Prefer `const` by default, use `let` if you need to reassign the variable. Avoid `var`.
- **Scope**: `var` is function-scoped, `let` and `const` are block-scoped.
- **Hoisting**: `var` declarations are hoisted and initialized with `undefined`. `let` and `const` are hoisted but not initialized (Temporal Dead Zone).
- **Re-declaration**: `var` allows re-declaration in the same scope. `let` and `const` do not.
Prefer `const` by default, use `let` if you need to reassign the variable. Avoid `var`.
answered about 2 years ago by
CHCharlie Brown