Correct scope outside a function in Javascript

Question

My question is regarding the below code:

var z='1'; 
(function(){ 
   y='2'; 
   console.log(z+y); // '12'
})();
console.log(z+y); // '12'

How come 'y' is accessible outside the function's scope?

Answer 1

You declared y like this y='2'; By not putting the var keyword in front of it, the variable automatically becomes global.

Answer 2

前面没有var的关键字被声明为全局变量。