javascriptiife

Why second console.log output is the function body rather than 20?

(function b() {
  console.log(b);
  b = 20;
  console.log(b);
})();

I wrote this JavaScript IIFE.
The first console.log logs the function body.
Then the b variable is created with value 20.
The second console.log also logs the function body.
Why not 20?

Solution

  • Because b is constant and cannot be assigned to. You're in non-strict mode, so the assignment just silently does nothing, but if you use strict mode you will get an error, highlighting the problem.

    (function b() {
  'use strict';
  console.log(b);
  b = 20;         // Throws an exception
  console.log(b); // Never gets to here
})();