Scope of locally defined function in javaScript

Question

I have this code snippet:

sayHi()

if (1) {
  function sayHi() {  alert(1)  }
} else {
  function sayHi() {  alert(2)  } // <--
}

How is it really working? The functions are defined in the if / else blocks. So how are they scoped outside the if / else blocks?

They aren't. When I run it, I get TypeError: sayHi is not a function — bejado
– bejado, Commented Feb 12, 2017 at 5:56

Barmar · Accepted Answer · 2017-02-12 05:59:14Z

1

The scope of the function is the entire containing function, because function declarations are hoisted. But the function doesn't get its definition assigned to it until the if or else block is executed. It's equivalent to:

var sayHi;
sayHi();

if (1) {
    sayHi = function() { alert(1); };
} else {
    sayHi = function() { alert(2); };
}

answered Feb 12, 2017 at 5:59

Barmar

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Comments

Jim Cote · Accepted Answer · 2017-02-12 05:58:08Z

0

Everything is scoped at the function level in Javascript, not the block level as with most other languages. So if you define a var in a for loop, it is "hoisted" to the top of the containing function.

answered Feb 12, 2017 at 5:58

Jim Cote

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1 Comment

Freyja Over a year ago

This is not completely true. var and function declarations are function scoped, but let, const and class declarations are block scoped.

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