What are the scopes of let/const and var? Is there another way to declare variables besides var, let, const?

Variable scope in JavaScript:

• var — has function scope. If declared outside a function, it becomes a global variable. The variable is accessible throughout the entire function body, regardless of block.

• let and const — have block scope. Variables are only accessible within the nearest curly braces (e.g., inside if, for, or function block).

Differences:

• var can be redeclared and reassigned within the same scope, while let and const cannot be redeclared; const cannot be reassigned.

Other ways to declare variables:

• Global variables without var/let/const — not recommended, but if a value is assigned to a variable without declaration, it is created in the global scope (will cause an error in strict mode).
• Declaration via function parameters — function parameters are also local variables.
• Declaration via import/export — in ES6 modules, variables can be imported or exported, which also affects scope.

Example:

function example() {
  if (true) {
    var a = 1; // accessible throughout the function
    let b = 2; // only accessible inside if
    const c = 3; // also block scope
  }
  console.log(a); // 1
  console.log(b); // ReferenceError
  console.log(c); // ReferenceError
}