web - scope of the variable in JavaScript -

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function foo(a) {   function a() {     return 8;   }   return a();   y = 9; } console.log(foo() + " " + y); 

this gives undefined error variable y.

function foo(a) {   y = 9;    function a() {     return 8;   }   return a(); } console.log(foo() + " " + y); 

this prints 8 9 in browser console.

if declare variable without var keyword becomes global variable.

why first function not follow idea?

it's because in first example, have return statement before y = 9 , assignment never reached, leaving undefined.