An issue about let statement in typescript.

[arliang]

http://www.typescriptlang.org/Playground#src=for(let%20i%20%3D%200%3B%20i%20%3C%2010%3B%20i%2B%2B)%7B%0D%0A%09setTimeout(function()%7B%0D%0A%09%09console.log(i)%3B%0D%0A%09%7D)%3B%0D%0A%7D

for(let i = 0; i < 3; i++){
    setTimeout(function(){
        console.log(i);
    });
}

for (var i = 0; i < 3; i++) {
    setTimeout(function () {
        console.log(i);
    });
}

In es6, the first example outputs 0 1 2
But the JS which translated by TS outputs 3 3 3

It would act like es6 if wrapped with (function(i){ /* */ })(i)

for (var i = 0; i < 10; i++) {
    (function(i){
        setTimeout(function () {
            console.log(i);
        });
    })(i);
}

[RyanCavanaugh]

This has already been implemented in #5208

[RyanCavanaugh]

Duplicate #3915