function-or-block-scope.md

Is JavaScript block-scoped or function scoped?

Short answer - Javascript is function scoped.

What is block-scoped?

Block-scoped exists when a declared variable has inside a block of code (usually enclosed between curly backets) is only visible/accessible within that block of code.

Consider the following.

var testFunc = function() {

  // printed it defined in the "for loop" block
  for (var n = 0; n < 10; n++) {
    var printed = n
  }

  // logging printed outside of block
  console.log(printed)
}

// logs 9 - printed is available outside of block
testFunc()

Thus Javscript is function scoped.

Or Not! It's a trick question!!!

With the introduction of ES6, const and let has been introduced as ways to declare/assign variables. Consider the following.

var testFunc = function() {

  // var is defined in the this for loop block
  for (var n = 0; n < 10; n++) {
    // notice use of let
    let printed = n
  }

  // logging printed outside of block
  console.log(printed)
}

// logs printed is not defined
testFunc()

Similarly

var testFunc = function() {

  // var is defined in the this for loop block
  for (var n = 0; n < 10; n++) {
    var printed = 1
  }

  // logging printed outside of block
  console.log(printed)
}

// logs 1
testFunc()

And

var testFunc = function() {

  // var is defined in the this for loop block
  for (var n = 0; n < 10; n++) {
    // notice use of const
    const printed = 1
  }

  // logging printed outside of block
  console.log(printed)
}

// logs printed is not defined
testFunc()

So Javascript also has block scoping.