Scope

Scope refers to the variables that are available to function. Where and how variables are established effects scope.

In JavaScript, a functions local scope includes:

  1. The functions parameters.
  2. Any variables established inside the function block.
  3. Any variables that were already available when the function was defined.

You should stick with let and const, as the lexical-style scoping here is more predictable.

//Variables in  Global Scope are accessible everywhere
let popularFruit = 'banana'

function changeFruit() {
  popularFruit = 'apple'
}
changeFruit()
console.log(popularFruit)
// => apple

// A new local scope is established in functions
// Local variables aren't available outside their scope
function newFruit() {
  var fruit = 'apple'
}

// This doesn't work:
// console.log(fruit)
// error! fruit is not defined

// let and const variables have block scope
// They're assigned to _any_ curly brace block
// including if, switch, loops, etc
function fruitLogger () {
  if (true) {
    const es6Fruit = 'blueberry'
    var oldSchoolJsFruit = 'pear'

  }
  // console.log(es6Fruit)
  // => error! fruit is not definied

  console.log(oldSchoolJsFruit)
  // => pear
}

fruitLogger()
$ node jsbyexample.js
apple
pear
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