Unusual javascript behavior -

i have encountered weird behavior in javascript. consider code:

var foo; function bar(){     function foo(){};     foo = 10;     return; } foo = 1; bar(); console.log(foo); 

this output 1. if delete foo function declaration in third line, output 10. why isn't output 10 when function declaration there? , reason if change function definition this:

foo = function(){}; 

it output 10 again? know hoisting of function declarations, doesn't seem answer this.

that's not weird - have variable called foo, you're setting 1 normally. inside bar function, foo function

• if present, shadows variable
• if not present, foo references original variable.

as such, if define foo function, foo=10 take effect on that, otherwise take effect on original foo.

as second part of question (why change if use var foo=...), that's because in case duplicate variable declaration merged one, end same if didn't write var.