What will the code below output to the console and why?

(function(){
var a = b = 3;
})();

console.log("a defined? " + (typeof a !== 'undefined'));
console.log("b defined? " + (typeof b !== 'undefined'));

Question

What will the code below output to the console and why?

(function(){
  var a = b = 3;
})();

console.log("a defined? " + (typeof a !== 'undefined'));
console.log("b defined? " + (typeof b !== 'undefined'));

Abdoulaye Siby · Accepted Answer

The output with show that a is not defined and that be is defined.

Here the reason why ...

The declaration line (var a = b = 3;) is inside of a function. Because of this, and due to the syntax used, only the `a` is seen as a local variable.

The variable `b` however is declared as a global variable. So onlye `b` will be seen outside the function.

The proper way to keep `a` and `b`local to the function would have been `var a = 3, b = 3;`

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