javascript - setTimeout is not working correctly inside "for loop" -

now of course, code make do.

but i'm confused why in following code:

var = {     0: "hi",     1: "bye" }  (var b in a) {     settimeout(function () {         console.log(b);     }, 1000); } 

instead of consoling "0" , "1"

i "1" twice.

i'm not sure why happens. need setup script making same issue.

it because usage of closure wrong.

in case using closure variable b inside settimeout callback, value of variable b not looked until callback executed, value of updated last value in object.

one of solution in such case create local closure given below

for (var b in a) {     (function(c){         settimeout(function () {             console.log(c);         }, 1000);     })(b) } 

demo: fiddle