ES6 Block Scoping

es6_block_scoping.js

// ES6 block scoping ('let' and 'const')
// 'let' example
// https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/let
if (true) {
  let foo = 'bar';
}
console.log(foo) // raises error: 'foo' is not defined

// Also prevents pass-by-reference errors in 'for' loops:
var funcs = [];
for(let i = 0; i < 5; i++) {
  funcs.push(function() { console.log(i); });
}
funcs.forEach(function(callback) { callback() }); // logs 0 through 4

// 'const' example
// https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/const
if (true) {
  // Use for constants
  const foo = 'bar';
  // Transpiler won't allow redefining foo within this block.
}
console.log(foo) // raises error: 'foo' is not defined

// ES5 compatible syntax transpiled by es6-transpiler
// https://github.com/termi/es6-transpiler
if (true) {
  var foo$ = 'foo'; // let and const both get renamed locally
}

console.log(foo); // outer scope variables retain old name