• Global scope — accessible everywhere in the file/program
• Function scope — var is confined to the nearest enclosing function
• Block scope — let/const are confined to the nearest { } block
• Lexical scoping — inner functions can access outer variables (the basis of closures)

let outer = 'I am outer';

function outerFn() {
  let inner = 'I am inner';
  if (true) {
    let blockScoped = 'only visible here';
    console.log(outer, inner, blockScoped); // all work
  }
  // console.log(blockScoped); // ReferenceError
}