What is the Difference Between "let," "var," and "const" in TypeScript?
In TypeScript, var, let, and const are used to declare variables, each with distinct behaviors regarding scope, hoisting, and mutability:
var:
- Scope: Function-scoped; accessible throughout the function in which it's declared.
- Hoisting: Variables declared with var are hoisted to the top of their scope and initialized with undefined, allowing access before declaration without causing errors.
- Re-declaration: Permits re-declaration within the same scope, which can lead to unintended overwrites.
let:
- Scope: Block-scoped; confined to the block () in which it's declared, enhancing control over variable accessibility.
- Hoisting: Variables declared with let are hoisted but not initialized, resulting in a ReferenceError if accessed before declaration.
- Re-declaration: Does not allow re-declaration within the same scope, preventing accidental overwrites.
const:
- Scope: Block-scoped, similar to let.
- Hoisting: Behaves like let in terms of hoisting; accessing before declaration throws a ReferenceError.
- Mutability: Requires an initializer and prevents re-assignment, ensuring the variable remains constant.
Understanding these differences is crucial for writing predictable and maintainable TypeScript code.