What&Why?

What will this do, and why?

Round 1 : Javascript

A) Alert “foo”
B) ReferenceError foo is not defined
C) Alert undefined

Answer

B - ReferenceError

Round 1: Javascript


  • A) Alert "1"
  • B) ReferenceError foo is not defined
  • C) Alert undefined

Answer

C - Alert Undefined


Why?

Here's another way of writing it:



variable declarations are 'hoisted' to the top of the function
(notice: function scoping, not block scoping)

Round 2: Javascript




  • A) Alert "I am a lizard"
  • B) ReferenceError foo is not defined
  • C) TypeError: undefined is not a function

Answer

C - TypeError: undefined is not a function


Why?



Variable declaration is hoisted, so it's there, but it's not a function yet.

Round 2: Javascript



  • A) Alert "I am a lizard"
  • B) ReferenceError foo is not defined
  • C) TypeError: undefined is not a function

Answer

A - I am a lizard

Why?


var foo = function() {} = function expression, only foo is hoisted
function foo() {} = function declaration, hoisted whole function


You can call functions declared with a function declaration from anywhere in the scope, but function expressions can only be called after they are assigned. 

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What&Why?

By Rod Howarth

What&Why?

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